School Science Lessons
22. Heat and temperature, candles, Joule's equivalent, boiling point, melting point, specific heat capacity, thermometers
2012-05-04b SP
Please send comments to: J.Elfick@uq.edu.au
Table of contents
22.2.0 Heat and temperature
22.6.0 Bunsen burner
22.1.0 Calorimeters
22.2.0 Heat and temperature
22.8.0 Heat sources (low cost equipment)
22.3.0 Heat transfer
22.10.0 Mechanical equivalent of heat, Joule's equivalent
22.4.0 Melting point and boiling point
22.5.0 Specific heat capacity, calorimetry
22.7.0 Thermometers and temperature
22.7.01 Commercial thermometers
22.7.02 Edited instructions for use of a "beurer" express thermometer FT15
22.6.0 Bunsen burner
22.6.1 Bunsen burner flame
22.6.2 Bunsen burner flame can melt copper wire
22.6.3 Bunsen burner safety
13.2.1 Flowing air can do work, flow pipe of uniform cross-section
2.11 Gas-pak
22.6.4 Hottest part of the Bunsen burner flame
22.6.5 Lighting a Bunsen burner
22.6.6 Study the Bunsen burner flame
22.1.0 Calorimeters
Calorific value of fuel: 4.38
Energy from food, bomb calorimeter: 6.6.17
Heat of neutralization with a simple calorimeter: 14.1.5.1
Simple calorimeter: 1.28
Specific heat capacity, calorimeter: 22.5.0
Test carbon dioxide as a greenhouse gas: 3.38.1
Voltage and current to a heating coil in a calorimeter: 33.5.6
22.2.0 Heat and temperature
22.2.0 Heat and temperature, joule, kilowatt-hour, kWh, calorie
4.5.0 Heat and temperature, experiments, UNESCO
13.0 Heat and temperature, experiments (Primary)
36.49 Angle of the Sun's rays on the Earth
4.38 Calorific value of fuel
22.6.0 Bunsen burner
22.1.0 Calorimeters
8.1.1 Candles, (Chemistry)
28.13.0 Candles, (Physics)
2.2.3 Electric kettle heating efficiency
22.2.3 Heat absorbed depends on mass
22.2.4 Heat dissipation
22.2.1 Heat has no weight
22.2.5 Heat solid sphere and hollow sphere
23.4.0 Materials at low temperature
22.4.0 Melting point and boiling point
22.2.6 Movement in hot water and cold water
4.3 Plug and ring experiment
2.8 Pressure affects the boiling point
12.1.3 Pressure on solid ice
6.3.1 SI, The 7 base units
7.7.5 Solubility of different salts and temperature
7.7.6 Solubility and temperature, plot solubility curves
29.1.6 Temperature and magnetism, Magnetism and temperature, Curie point
4.31 Temperature of water at maximum density, 4oC
6.3.1.5 Temperature, Celsius scale, Kelvin scale, Fahrenheit scale
4.1 Temperature rise and quantity of heat intake
22.3.0 Thermometers and temperature
4.2 Transfer kinetic energy to heat energy
22.8.0 Heat sources
1.33 Air oven
22.1.2 Drink-can charcoal burner
1.21 Electric hot plate
4.65 Electric light bulb, incandescent filament lamp, light globe
29.2.7.5 Magnetic stirring hot plate
1.31 Metal can heater
22.1.1 Simple heater
2.20 Spirit burner, alcohol lamp, (Primary)
8.1.3.1 Spirit burner, alcohol lamp
1.18 Wax taper
22.3.0 Heat transfer
2.1.5 Heat insulation properties of common materials
4.2.2 Heat one litre of water from room temperature to 100oC
22.2.7 Heat transfer and laws of thermodynamics
22.2.8 Heat transfer by Dewar flask (vacuum flask, "Thermos" flask, Mariotte flask)
22.2.7.1 Heat transfer coefficient, 1 / thermal insulation
23.8.23 Melting blocks of ice
22.10.0 Mechanical equivalent of heat, Joule's equivalent
22.10.0 Mechanical equivalent of heat
22.10.7 Mechanical equivalent of heat, J, by an electrical method
22.10.2 Dropping lead shot
22.10.6 Flint and steel
22.10.5 Friction ignition, bow and stick, fire maker, drill and dowel
22.10.3 Hammer on lead
22.10.4 Heat by bending
22.10.1 Waterfall
22.4.0 Melting point and boiling point
7.5.0 Boiling point, b.p.
7.4.0 Melting point, m.p.
24.1.0 Phase changes liquid / solid, melting point and freezing point
7.7.5 Solubility of different salts and temperature
22.5.0 Specific heat capacity, calorimetry
22.5.0 Specific heat capacity, (heat capacity, specific heat, thermal capacity), C
22.5.8 Candle burns below water level
6.6.17 Energy from food, bomb calorimeter
22.5.3 Heat capacity (water equivalent)
22.5.03 Heat capacity (thermal capacity) C, of a calorimeter
22.5.7 Heat of combustion, bomb calorimeter
22.5.6 Ice calorimeter
22.5.1 Melting wax calorimeter
22.5.4 Mix heated water
22.5.02 Molar heat capacity, Cm
22.5.5 Specific heat calorimeter
22.5.01 Specific heat capacity, shc
22.5.2.1 Specific heat of aluminium by electrical method
22.5.01 Specific heat of water
22.5.2 Specific heat of water by electrical method
22.7.0 Thermometers and temperature
22.7.0 Thermometers, commercial thermometers
22.7.8 Air thermometer
22.7.2 Expansion of liquid in a thermometer
22.7.7 Galileo's thermometer
4.14 Test a liquid in glass thermometer
4.15 Thermoscope to compare absorption of radiation
22.7.4 Thermometer, 0oC to 100oC range
22.7.5 Thermometer, make a thermometer
22.7.1 Temperature sense, feeling "warm" and "cold", measure temperature correctly only with thermometer
22.7.3 Thermometer test, calibrate a thermometer
22.7.6 Thermocouple, thermistor, constantan, optical pyrometer
1.18 Wax taper
Wax taper, gas lighting, pack / 55
1.21 Electric hot plate
Electric hot plate, 240 V, AC 600 watts, 200 × 100 mm, high temperature alloy plate, "Simmerstat" temperature control, maximum plate temperature approximately 450oC, 215 × 185 mm
1.28 Simple calorimeter
See diagram 22.1.8: Simple calorimeter
1. Use a large-mouth glass bottle for example a large coffee bottle. Use a can with a top only able to be opened by a rotating knife to make sure that the outer rim on the top may be reserved in good order. and if place the bottle into the can make sure that the distance between the bottom of the can and the bottom of the bottle must be more than the distance between the outside of the can and the inner wall of the bottle. so that there is enough air between the can and the bottle to insulate heat. Twine a circle of a narrow piece of foam (or sponge) at the upper outside of the can. Use white adhesive plaster to paste the foam to prevent the foam from slopping. Make a round cover with a white rigid used to pack instrument foam board (or middle density board). Do not use a scroll saw dig a round on the rigid plastic board. You may cut off a square first with a knife cutting paper then cut it into a round. Use 0.15 cm wire to make a beater with a thermometer and brass wires. Drill a hole on the cover. To prevent heat loss paste a circle of silver paper metallic surface inwards then put some paper between the bottle and the can.
2. Simple calorimeter
Small soup tins can be found which fit loosely into a jam jar. If the top of the tin is cut off cleanly with a rotary type opener it serves as an excellent calorimeter. The metal can be prevented from slipping into the jar either by a stout rubber band round the edge, or by cutting nicks in the rim and bending it slightly outwards. This form of suspension, and the low conductivity of glass and air contribute to its efficiency. Expanded polystyrene, Styrofoam, drink cups are available in some countries and make excellent calorimeters. Other suitable calorimeters can be made using two metal cans or glass beakers. Select containers so that one will fit inside the other with at least 1 cm of space between them. Fill this space with glass wool or crumpled paper.
1.31 Metal can heater
See diagram 23.1.3
A heater can be made from an old oil tin. Water is placed in the tin and heated from below. Iron wire is wrapped round a test tube and twisted to form a handle. The substance to be heated is placed in the test tube
1.33 Air oven
See diagram 23.33
A large metal can be used as an air oven. A hole through the lid fitted with a cork holds a thermometer, and the saucer or dish rests on a wire gauze bridge placed inside the tin.
2.8 Pressure affects the boiling point
Use a flask with a one-hole stopper with a thermometer in it. Fill a flask 3/4 full with water, add boiling chip, heat until boiling, read the temperature, about 100oC. Invert the flask and hold it under a cold stream of water. The water boils again. Read the temperature, less than 100oC. Again invert the flask and hold it under a cold stream of water. The water boils again. Read the temperature, less than before. When the flask is cooled off with the cold water, water vapour in the flask above the water condenses on the colder surface of the flask, a partial vacuum forms and the pressure inside the flask decreases. Water boils at 100oC at standard pressure, i.e. 760 mm mercury or the pressure at sea level. If the pressure is lower the boiling point is lower. So it is hard to make a good cup of tea on a high mountain because the water boils at such a low temperature.
2.112 Temperature sense, feel temperature
Check if your temperature sense is reliable. Use containers of hot water, warm water and cold water. Put both hands in the warm water. The hands feel the same temperature. Put one hand in the hot water and the other hand in the cold water. Quickly dry your hands and put them both into the warm water again. The two hands do not feel the same temperature. Is your temperature sense reliable? This may be a silly experiment but it shows that your temperature sense is not always reliable. You must use thermometers for experiments.
2.113 Thermometer, expansion of liquid in a thermometer
Fill a flask with coloured water. Insert a one hole stopper carrying a 30 cm length of glass tubing until the water rises 5 cm in the tubing. Put the flask in a beaker of water. Heat the beaker and observe the water level in the tubing. The water rises in the tubing. However, if you carefully observe the water level in the tubing when the heating begins, you will see that it falls slightly and then begins to rise! It falls because the glass in the flask starts to expand before the water inside. When the heat energy reaches the water it expands. So the expansion of liquid you see in a thermometer is really the expansion of liquid less the expansion of the glass tube.
2.114 Spirit thermometer Experiment deleted!
Make a spirit thermometer by blowing a bulb in one end of the tubing, inverting the open end of the tube in alcohol. Alternately heat and cool the bulb to draw alcohol into the tube, then calibrate in containers of water of known temperature. However, this activity is too dangerous for schools especially when it comes to heat sealing the tube.
2.115 Test a thermometer
Use a thermometer with a scale, e.g. thermometer -10oC to 110oC mercury or alcohol, or a tall flask containing coloured water fitted with a one hole stopper and glass tube that extends into the bottle. Mark thermometer scales at two fixed points. The lower fixed point is the temperature of melting ice. Put the bulb of a thermometer in crushed ice that is melting. Leave it there for some minutes. Check that the temperature is 0oC on the calibrated thermometer, or make a mark on the blank scale or on the glass tube attached to the small flask. The upper fixed point is the temperature of boiling water. Put a thermometer in steam immediately above the surface of boiling water. Leave it there for some minutes. Check that the thermometer reads 100oC on the calibrated thermometer, or make a mark on the blank scale or on the glass tube attached to the small flask. Divide the distance between the upper and lower fixed point to obtain marks representing a temperature difference of 1oC. If you do the experiment on a mountain at high altitudes the temperature of boiling water may be below 100oC because of the reduced atmospheric pressure. If you do the experiment in a submerged submarine the temperature of boiling water may be above 100oC. The thermometer in the boiling water reads exactly 100oC only at sea level or where the barometer reading is 760 mm of mercury.
4.1 Temperature rise and quantity of heat intake
See diagram 23.103 Temperature rise and quantity of heat intake
1. Put a large iron bolt and a nut for the bolt in a container of boiling water to bring them to the same temperature. Put equal volumes of water in two containers with each volume enough to immerse the bolt. Put the hot bolt in one container and the hot nut in the other container. Record the temperature of the water in each container after the same period. The difference in temperature change of the water in the two containers is because of the different amounts of heat stored in the iron bolt and the iron nut.
2. Check if your temperature sense is reliable. Use containers of hot water, warm water and cold water. Put both hands in the warm water. The hands feel the same temperature. Put one hand in the hot water and the other hand in the cold water. Quickly dry your hands and put them both into the warm water again. The two hands do not feel the same temperature. Is your temperature sense reliable? This may be a silly experiment but it shows that your temperature sense is not always reliable.
4.2 Transfer kinetic energy to heat energy
See diagram 23.104: Transfer kinetic energy to heat energy
Use a small piece of lead sheet wrapped around one end of a piece of thin iron wire. Hold the other end of the wire. Hit the lead several times with a hammer. Feel the temperature rise as heat moves along the wire towards your hand.
4.8 Expansion of air
See diagram 23.110: Expansion of air
1. Use a flask fitted with a one-hole stopper and glass tube that extends into the flask. Put a small amount of oil in the glass tube to trap air in the flask. Hold the flask in your hands. The oil moves up the tube because the heat from your hands causes the trapped air to expand. If you look carefully note that the oil first moves down because the heat from your hands first causes the glass of the flask to expand. When you cool the flask under the tap, the oil moves down.
2. Fit a hard glass test tube with a one-hole stopper that has a length of glass tubing through it. Invert the test tube so that the end of the tubing is in a container of water. Clamp the test tube in an inverted position so that you can heat it with a burner. Heat the test tube and note the bubbles from the end of the tube in the container of water. Heat has caused the air to expand. Cool the test tube by pouring cold water over it. Water moves up the glass tubing as the cooling air contracts.
3. Fit a toy balloon over the neck of a small flask. Put the flask in a container of water. Heat the water. The balloon expands as the heated air in the flask expands. Partially inflate a balloon and tie the neck tightly. Leave it in a warm place or in the sunlight. The balloon becomes fully inflated as the air inside expands when heated.
4.9 Burn candles over water (expansion of air when heated)
See diagram: 3.1.4.5: Burning candles over water
See 6.35: Burn candle over water, candle burning in inverted jar over water
Attach a tall candle and a short candle to the bottom of a trough. Add water to the trough and note the water level. Light both candles. Put a large jar upside down over the candles. The tall candle extinguishes first then the short candle. Hot gas products of combustion including carbon dioxide gas have filled the jar from the top down to extinguish the candle flames. Some hot gases push out under the rim of the jar to form bubbles around the jar in the trough. When the candles are extinguished, the hot gases cool and contract to form a partial vacuum and the water level rises inside the jar.
Some decrease in volume will be caused by the candle wax burning to form carbon dioxide and water. Some of the carbon dioxide will dissolves in the water from the trough and the water vapour formed will condense to form liquid water. More air escaped from the jar in the beginning due to large amount of heat released by the two candles.
When we ignite the candle, the stearin (purified fatty acids) reacts with oxygen (in excess) to produce carbon dioxide and water. The burning causes air currents to shape the candle flame and ensure complete combustion at the bottom and the outer surface of the flame. The hot air and products of combustion rise up above the flame. When a jar is placed over the burning candle the hot gases in the jar expand and pushing some of the air out of the jar as bubbles in the water. As soon as the rim of the jar touches the water, the burning occurs in a closed environment. Further pressing the jar down into the water helps to retain the hot air in the jar under a pressure greater than than atmospheric pressure and balanced by the pressure of the depth of water.
The burning of hydrocarbon in the jar produces more molecules of carbon dioxide and water than the molecules of oxygen consumed in the reaction. The increased heat and number of molecules increases the pressure in side as a result if not careful some bubbles of gas will escape from the jar. Over the time the oxygen in the jar is reduced and conditions for burning are changed. Burning under reduced oxygen may not produce carbon dioxide rather a little carbon monoxide. When the candle is put out, the temperature decreases followed by also a decrease in pressure due to condensation of water vapour and decreased quantity of air due to thermal expansion during the process of placing the jar on the candle. The overall situation is a decrease in pressure inside the jar as compared to atmospheric pressure so despite water being heavier that air, it is pulled into the jar. A negligible amount of carbon dioxide is dissolved in the water during 30 - 40 minutes, the time the experiment usually takes for performing in a classroom situation. If the number of candles is increased in the jar, the heat produced is more therefore more air is likely to escape from the jar due to thermal expansion during the process of pacing the jar over them. Therefore, more water will rise in the jar with more candles.
The nature and quantity of the products will depend upon the composition of candle material. However, it is assumed that combustion of saturated hydrocarbons is taking place during burning. For the paraffins in the stearin candle, chain length, n = about 30
During combustion the solid stearin combines with 3 volumes of oxygen gas to form e volumes of carbon dioxide e gas + 2 volumes of water vapour
So the expansion of gases caused by this chemical reaction = 4/3 = 1.3'
2CH2 (s) + 3O2 (g)--> 2CO2 (g) + 2H2O (g)
However, after the candles are extinguished, drops of water appear on the inside of the jar caused by condensation, so 3 volumes of oxygen have produced 2 volumes of carbon dioxide, a contraction of 2/3.
Previously, teachers taught that the candle become extinguished because all of the oxygen under the inverted jar "was used up", i.e. converted to carbon dioxide, and so the decrease in volume of air under the jar after the candles are extinguished indicating the proportion of oxygen in the air. However, some oxygen remains in the inverted jar as can be demonstrated by testing with yellow phosphorus.
The rapid rise of water level in the jar after the candles are extinguished is caused by decrease in pressure as the hot gases cool and the condensation of water vapour. The amount of condensation of water will depend upon the temperature difference between initial and final temperatures of the air in the jar. Since air is above water, therefore saturated water vapour pressure is considered in the beginning of the experiment. Increase in temperature, during the candle burning, will make air unsaturated to accommodate additional water vapours especially produced as a product of burning. A decrease in temperature over time after the candle is off to the initial temperature will help water vapour to condense. This condensation will decrease the pressure inside the jar and will help water rise in the jar. The amount of water vapours condensed during a small change of temperature as usually occurs in this experiment may even be small to notice.
Some teachers believe that all the oxygen is consumed during combustion before the candle is extinguished and the water rises in the jar to fill in vacuum created by consumption of oxygen. They do not expect the air to escape from the jar as a result of thermal expansion. They believe that one candle will burn longer in the jar than two candles. The water level in jars with one or two candles will rise to the same level because the amount of oxygen in the jars is the same, about 20%.
A little carbon dioxide dissolves in the water during the experiment. A jar full of carbon dioxide inverted over a trough of water does not completely dissolve after some days. To study the level of water rise when the candle was put out as soon jar touched the water, a floating candle was used and it was made to sink as soon as jar touched the water in the trough. It was found that water did rise to some extent, indicating that some air escaped from the jar because hot air and burning products entered the jar from the candle during the process of placing the jar over the candle. The oxygen in the jar after the candle was extinguished produced rust in steel wool, reacted with yellow phosphorus to produce white smoke of oxide and supported survival of a mouse and insect for a long time. To test whether the presence of carbon dioxide or lack of oxygen extinguishes the candle, remove the carbon dioxide from the jar by using sodium hydroxide solution in the trough in place of water. Also you can spray cotton wool with sodium hydroxide and attach it to the bottom of the jar before it is inverted on the candle. The candle burning time was almost doubled indicating that it is the presence of carbon dioxide that extinguishes the candle. When a candle burning under a jar inverted over water in a trough was repeated using two and three candles. The level of water in the jar increased with an increase in number of candles. This finding was used to emphasize that more oxygen is escaped from the jar before or during the burning of candles. However, it is not true that more oxygen was consumed with the increase in the number of candles.
12.1.3 Pressure on solid ice
Use 1 m thin strong steel wire, e.g. piano wire. Attach each end to a broom handle. Loop the wire round a block of ice it and pull tightly so that the wire exerts pressure on the ice. The pressure causes the ice to melt but when the pressure is released the ice becomes solid again. Apply pressure and observe how the wire makes its way slowly through the ice. Similarly a knife forced against ice can exert pressure enough to melt the ice at the edge of the blade. Force cubes of ice together then see them join when the pressure is released and the melted ice freezes again. An ice skater skates on a thin layer of water!
22.1.1 Simple heater
See diagram 22.1.1: Simple heater
Make a heater from an old oil tin can. Fill the tin can with hot water and heat from below. Wrap wire around a test tube then twist it to form a handle. Put the substance to be heated in the test tube.
22.1.2 Drink-can charcoal burner
See diagram 23.1.1: Simple heating devices
Prepare a large can of diameter at least 10 cm. Draw 6 small windows of regular triangle uniformly on the side of the can and an angle of each triangle just up just towards the bottom of the can. Each window locates at the centre of the side of the can. For each triangular window cut off the two lines of the angle downward then bend the triangular sheet back. The 6 triangular sheets form a stand in the can. Charcoal may be placed on the stand. Polish the windows with a file and drill some air holes. Now a stove has been made.
22.2.0 Heat and temperature, joule, kilowatt-hour, kWh, calorie
Internal energy and heat, thermal physics, thermal properties of matter, heat as a form of energy
1. The distinction between internal thermal energy, heat energy and temperature. Heating is a process by which internal energy transfers occurs as the result of a temperature difference.
2. Heat is a means by which energy can be transferred. The numerical value for the heat is the amount of energy transferred. Internal energy is the energy associated with the total kinetic and potential energy of all of the molecules of the object. If energy is transferred to an object its internal energy rises. The internal energy would also increase if work were done on the object. The SI unit of heat energy is the joule (i.e. newton.metre). The extent to which an object will transfer or absorb heat (its hotness or coldness) is measured by temperature and is related to the average kinetic energy of its molecules. The process by which the energy is transferred as heat as one of the following three: convection conduction and radiation.
3. The joule, J, is the SI unit of work and energy. A joule is equal to the amount of work done when the point of application of a force of one newton moves one metre in the direction of the force.
1 Joule of work done = 1 newton force moves object through 1 metre
Work done = force distance in direction of force, W = Fs
Work and Energy
Work = force × distance (displacement), joule (newton.metre). Work done on an object changes its energy that may be stored as potential energy or cause change in speed, kinetic energy. When a wheel is moved by a force, the work done = displacement × component of the force in the direction of the displacement
4. The CGS (cgs) unit, the calorie, is the amount of heat required to raise the temperature of 1 gram of water by 1oC at 15oC (room temperature), i.e. 1 K.
1 calorie (cal) = 4.184 J, commonly, 4.2 joules. 1 joule = 107 ergs = 0.2388 calorie. Nowadays the SI unit the joule, J, is used.
5. You may see "kilocalories", 1000 calories, in nutritional information about weight loss. In some "calorie counter" books, 1000 calories is a "Calorie", so in their tables 1 "Calorie" = 4.2 kilojoules.
6. The kilowatt-hour, kWh, is the energy used when when an appliance with the power of one kilowatt runs for one hour. A power of one watt = one joule per second, so a kilowatt-hour = 3,600,000 J, about the energy used by one bar of an household electric heater.
1. Suspend a metal can containing 50 mL water and a thermometer over a small Bunsen burner flame or a candle. Record the initial temperature. Heat it for two minutes, constantly stirring, and record the final temperature in degrees Celsius, oC. Empty the water and repeat the experiment with 100, 150, 200 mL water, using the same flame. Assume 1 mL (1 cm3) water = 1g. Find the product of mass of water × by rise in temperature. As the same heat is given out by the flame to each mass of water (100, 150, 200 mL), a convenient unit of amount of heat would be the amount of heat absorbed by 1 g water rising in temperature by 1o C. This unit is the calorie or gram calorie.
22.2.1 Heat has no weight
The recognition of heat by people in history had experienced a long and tortuous way. So called "heat mass" in general shows a unclear recognition to the character of heat. Heat is a form of energy has no weight. However, some students are probably think that heating a beaker will somehow make it lighter. A few may believe that putting "heat in " somehow makes the beaker heavier! Hang a spoon in each end of the cross arm in a stand thread tie to the spoon must be strong enough. Adjust the position of spoon to get them in exactly balance. Record these two positions. Then remove the spoons. Heat one of the spoons by lifting it over an alcohol burner. Put another spoon into cold storage in a refrigerator or cold water (if use refrigerator it is better not to put spoon into freezer). Place the two spoons back to the original position exactly note to affirm the cooled spoon is dry in advance and the position must be original one. To ensure not to confuse them it is better to select the two spoons which have different sizes and shapes or use different colour thread to tie them. If every step is done the whole system is still in balance. To avoid marking in cross arm to mark the original position the cross arm can be replaced by a meter.
22.2.3 Heat absorbed depends on mass
Place a large iron bolt and a small nail in a beaker filled with boiling water. Fill other two beakers with equal masses of cold water at same temperature put a thermometer each. Note that the amount of water is better to just immerse iron bolt. To do this you can test a suitable the amount of water by bolt before experiment. In the process of the experiment let large iron bolt and small nail are in boiling water for a while then take them out of boiling water. Put large one into a beaker small one into another beaker rapidly. Observe the temperature of water rises record the temperature in each beaker after temperature is stable. The different temperature shows the different amount of heat they have. The objects in different masses at the same temperature absorb amount of heat which depend on their mass each.
22.2.4 Heat dissipation
Fill a small and a large round bottom flask with hot water at the same temperature. Insert thermometers in both flasks and note the decrease in temperature as heat is dissipated. Heat dissipation is a function of of the area of the surface. Heat content is a function of he volume of the unit. The area increases as the square of the radius but the volume increases as the cube of the radius.
22.2.5 Heat solid sphere and hollow sphere
Put a solid metal sphere and a hollow metal sphere with the same external volume in a beaker of water and heat the water. The expanded external volumes are still the same. Put the two spheres in identical beakers and add the same volume of water heated to the same temperature. The hollow sphere expands more than the solid sphere because its mass is less.
22.2.6 Movement in hot water and cold water
1. Prepare two sources of hot water and cold water with ice floating in it. Hold a needle, point down, and, exactly vertical, above two paper cups. Push the needle down through the bottom of the two paper caps to make exactly same size holes. Pour the same volume of hot water or cold water into the paper cups. Watch the drips of water from the holes in the paper cups. The hot water leaks faster than the cold water. The molecules of the hot water are moving faster than the molecules in the cold water so they can move past each other more quickly and more quickly move through the hole in the bottom of the paper cup.
2. Prepare two identical beakers containing the same volume of hot water or cold water. Put two drops of ink or colouring, e.g. cochineal, into each beaker. Observe the time taken for the drops to spread throughout the water. The colouring in the hot water spreads faster because the water molecules are moving faster around each other.
22.2.7 Heat transfer and laws of thermodynamics
Heat is a form of energy. The unit of work and energy is the joule, J, (i.e. newton.metre) (James Prescott Joule 1818 - 1889).
Heat transfer by conduction, convection and radiation, coefficient of expansion, the joule / calorie
1. First law of thermodynamics: When other forms of energy are converted to heat or when heat is converted to other forms of energy there is no loss of total energy.
2. Second law of thermodynamics: Heat always flows from hot bodies to cold bodies.
Heat is a form of energy measured in joules, J. Heat transfer is the process of transfer of energy from an object to another, or from a part of an object to another one. Heat energy can be transferred by conduction, convention, and radiation. The natural flow of heat is from higher temperature towards lower temperature. So heat energy spreads out from concentrations at high temperature. When you apply heat to one end of a solid conductor, the particles at that end, e.g. atoms and molecules vibrate more rapidly. This energy is passed from particle to particle through the material by conduction. All metals are good conductors of heat but many liquids and gases are poor conductors. Liquids and gases can transfer heat by convection when hot fluid rises and is replaced by colder surrounding fluid. Heat can be transferred through space as electromagnetic radiation. Rough or black surfaces are good absorbers and good emitters of radiation whereas polished or white surfaces are not.
22.2.7.1 Heat transfer coefficient, 1 / thermal insulation
Heat transfer usually by convection between a fluid and a solid or by phase change
h = q / A × δT
h = heat transfer coefficient, W / (m2K), watts per meter2 Kelvin
q = heat flow, in or out, J / S = W
A = surface area of heat transfer
δT = temperature difference of solid surface and fluid area (T1 -T2)
Heat transfer coefficients
Aluminium 237, Brass 110, Copper 398, Glass 0.96, Ice 2.18
Convective Heat Transfer Coefficients
Free Convection, Air : 5 - 25 W / ( m2K)
Free Convection, Water: 20 - 100 W / ( m2K)
Rate of heat transfer, R = K × area (T1-T2) / thickness
22.2.8 Heat transfer by Dewar flask (vacuum flask, "Thermos" flask, Mariotte flask)
See diagram 23.05: Dewar flask
1. A thermos flask is a double walled vessel, the space between the walls being a near vacuum. Heat cannot be conveyed through the two walls by conduction and the air cannot get into direct contact with the inner wall, so that heat is not conveyed away by convection. The outer side of the inner vessel and the inner side of the outer vessel are silvered to reduce the loss or gain of heat by radiation. The vessel is fitted with a cork or plastic stopper to prevent heat transfer by convection at the top and the loss of heat by conduction through the bad conductor cork or plastic..
2. The silver surfaces of the double glass walls or steel walls reduce radiation. The thin walls of the double glass flask, the vacuum between the double walls and the cork or rubber stopper reduces conduction and prevent evaporation. The case reduces convection.
3. Draw a cooling graph for a vacuum flask. Almost fill a vacuum flask with boiling water. Note the time and temperature of the hot water every half hour until it is cold. Draw a graph of your results. When the contents are hot, heat is lost at a greater rate so the temperature-time graph is a swooping curve rather than a straight line. Thus heat losses are faster when the difference in temperature between the hot object and the surroundings is greatest. Put an equal quantity of ice cold water in a second vacuum flask it and graph the rate of warming. A vacuum flask keeps heat from getting out from hot things and stops heat from getting in to cold contents.
4. Keep a broken thermos flask in a safe place in the laboratory store room so that the walls of the thermos flask may be examined.
22.6.1 Bunsen burner flame
See diagram 3.1.4.2: Bunsen burner | See diagram 3.1.4.0: Bunsen burner flame | See diagram 3.2.1: Burning the gas in a cone of flame
1. Study the flame of a Bunsen burner and a candle. A flame is the region where combustion occurs. The colour of the flame depends on the temperature and the substance burning. Hydrocarbon flames are either blue or yellow. A blue flame is a not luminous and occurs because of complete burning of hydrocarbons with plenty of oxygen gas. The flame does not leave any residue or any other gases. A yellow flame occurs when there is insufficient oxygen gas. It is a luminous flame. The temperature is lower than the blue flame and leaves black soot and other residues. A candle contains wax made from petrochemicals. The wick is lighted, and this melts the wax. The evaporated wax rises and catches fire. As the vapours rise higher, they stay longer in the hot regions of the flame and start burning completely with oxygen gas. The candle flame has three regions. The inner zone appears black, contains unburned wax vapours and is the least hot region of the candle. The middle zone is where the wax vapours start burning giving a yellowish flame of partially burnt gases because of insufficient gases for complete combustion. The flame is a luminous region but not very hot. The outer zone is where the wax vapours have enough oxygen gas to burn completely. The flame appears blue and the temperature is very high.
2. This type of gas burner has a gas jet at the base that draws air in through the air hole because of the Bernoulli effect. It was invented by German chemist Robert Bunsen to improve the efficiency of combustion by combining flammable gas from a jet with air before ignition to give a very hot flame. This premixed flame has a different structure to the diffusion flame of the candle. The blue part of the flame in inside the flame. The flame is conical because of the shape of the rim of the burner. The premixed flame burns efficiently with not much yellow flame or production of soot.
3. Control the amount of air by opening and closing the air hole. Close the air hole. Turn on the gas. Light the gas. The flame is yellow. Hold a piece of wire in different parts of the flame to discover which part is the hottest. Hold a splint in different parts of the flame. The splint can be set alight in all positions in the yellow flame. Hold a test tube just above the flame. Carbon is deposited on the glass. Test whether the unburned carbon causes the yellow colour of the flame by sprinkling powdered charcoal (carbon) into the flame. Open the air hole. Mixing the air with the gas allows the gas to burn more rapidly and completely. The flame has an outer cone of mainly blue flame and a colourless inner cone. The outer cone has a thin colourless area outside the blue flame. Hold a splint so that it passes through the inner cone of the flame. The middle of the splint does not burn because the inner cone is mainly unburned gas. Hold a piece of wire in different parts of the flame to discover which part of the flame is the hottest. The tip of the colourless part around the outer cone is the hottest part of the flame. The temperature of different parts of a Bunsen burner flame can be measured with a thermocouple.
4. Test the inner cone of the flame
Put one end of a piece of glass tubing in the inner cone of the flame. Ignite the unburnt gases that come out of the other end of the tube.
Commercial
Bunsen burner, suits PVC tube
Bunsen burner, L.P. gas
Bunsen burner, natural gas
Semi micro Bunsen burner with flame retention collar, rotatable air regulator, and gas inlet tube, 100 mm height, natural gas
22.6.2 Bunsen burner flame can melt copper wire
See diagram 3.1.4.1: Bunsen burner flame
Bunsen burner flame can melt lead, m.p. = 327oC, and zinc, m.p. = 419oC. Many people think the temperature of a flame cannot exceed 500oC. Copper melts at 1085oC. It is not usually considered possible to melt copper with a Bunsen burner flame. The temperature of different parts of a non-luminous flame, a blue flame, with the air holes fully open, vary. The hottest part of the flame is at the tip of the central cone. The central core of the flame contains a mixture of unburnt gas with air. The intense blue region surrounding the central core is the main zone of combustion, in which the gaseous hydrocarbon fuel reacts with the oxygen, forming short-lived gases. The lighter blue outer flame is where these short-lived gases are completely oxidized to carbon dioxide and water. Copper metal reacts readily with oxygen from air when heated strongly, forming a coating of black copper oxide, CuO. Under reducing conditions, black copper oxide is reduced readily to metallic copper. When heated strongly, but below its melting temperature, copper glows with a bright red heat. To show that the maximum temperature reached, you can melt copper use pieces of copper wire with three different thickness found by stripping the insulation from electrical flex.
1. Light a Bunsen burner, turn the flame to maximum height, and open the air holes so that the flame is completely blue. Hold a piece of thick copper wire with tongs and probe the flame with the wire 1. starting from the bottom 2. around the sides and tip of the central cone, and 3. around the outer blue flame. At each place, record the appearances of the copper, e.g. black, orange, red hot, or tending to melt.
2. Repeat the process with a thinner piece of copper, then with a very thin piece of copper wire.
3. Reduce the flow of gas and repeat the procedures with a smaller blue flame. The flame has six separate zones: Zone 1 is the core of unburnt gas and air at the base of the flame. Zone 2 is the bright blue region of intense combustion surrounding the core: zone 2A is the tip of the central core, zone 2B is the region at the sides of the central core. Zone 3 is the outer region of the flame where combustion becomes complete: zone 3A is at the top of the flame, zone 3B is the outer part of the sides of the flame. Zone 4 is the region just outside the flame. At each zone observe the appearance of the copper, e.g. black, orange, red hot, tending to melt, three different thickness of wire. You can melt fine copper wire in the flame but not thick copper wire.
22.6.3 Bunsen burner safety
See diagram 3.1.4.1: Bunsen burner flame | See diagram 3.1.4.2: Bunsen burners
Be careful! Do not turn the gas on without lighting the Bunsen burner. Gas forms an explosive mixture in air.
1. Combustion is the burning in oxygen gas of a substance to produce heat and sometimes light energy. A flame appears during combustion when a gas has such a high temperature that it emits heat and light. A flame appears only where the burning gas and oxygen gas are in contact.
2. The Bunsen burner consists of 2.1. a barrel, shaft, 2.2 an air regulator, i.e. a sleeve with a hole in it, 2.3 a jet, air mixture valve, needle valve, 2.4 a base, 2.5. a gas inlet opening.
3. Adjust the flame by opening or closing the gas tap. When the air regulator is open, the gas burns with a noisy blue flame that may be nearly invisible in strong light. If the flame rises up from the burner, turn down the gas supply.
4. When not using the Bunsen burner, either turn off the gas or close the air regulator to give a safety flame. The flame is yellow because of the incandescence of carbon particles. It is not as hot as the blue flame and leaves black soot deposits on glassware.
5. Regularly inspect gas fittings on the benches and hoses connecting Bunsen burners to gas turrets to make sure that connections are free of leaks. With paired gas outlets make sure that only the gas tap connected to the Bunsen burner is turned on.
6. Tests for leaks by dipping the part in soapy water. Be careful! Do not use a lighted match.
7. Heat flammable liquids in water baths using electrical hot plates, not Bunsen burners. Turn the gas off first at the gas tap, then at the cylinder or main supply tap.
8. Use the Bunsen burner only in a draught free area, away from wall fittings and blinds. Allow the Bunsen burner to cool before you move or store it.
9. Do not heat low melting point objects, e.g. plastics, solder, lead, over the barrel of the burner. Melted pieces may fall inside the barrel. Hold the burner at an angle. If a match is blown out, turn gas off, then light the Bunsen burner again.
10. When not in use, turn off Bunsen burners to limit the production of carbon monoxide.
22.6.4 Hottest part of the Bunsen burner flame
See diagram 3.1.4.1
Add 3 cm of water and small boiling chips to 3 test tubes. Measure the time taken to boil the water when the bottom of a test tube is held at the top of:
1. yellow flame (air hole closed), 2. non-luminous (dark blue) flame (air hole open), 3. light blue flame (air hole open). The test tube held at 3. boils the soonest.
22.6.5 Lighting a Bunsen burner
See diagram 3.1.2: Right and wrong ways to use a Bunsen burner
1. Close the air regulator, light a match, hold the match flame at the side of the barrel opening, turn the gas tap on, raise the match flame to light the gas. The gas burns with a visible yellow flame, a quiet safety flame. Hold a test-tube just above the flame. Note the carbon (soot, carbon black) that deposits on the glass. To test whether unburned carbon gives the yellow colour to the flame, sprinkle powdered charcoal on the flame and compare the yellow colours.
2. Start to open the air regulator until the gas burns with a medium blue flame with a light blue inner cone and a pale violet outer flame with a bushy appearance. The flame has an outer oxidizing zone where combustion is complete, a middle reducing zone, and an inner unburned gases zone surrounded by a blue cone. This flame is the most useful for heating. Fully open the gas regulator until you get a roaring blue flame with a light blue triangle in the centre of the blue cone.
3. Open the air regulator. Keep turning down the gas supply. The gas "blows back", "strikes back". The gas is burning inside the barrel. Turn the gas fully on and strike the gas supply rubber tube with a sharp blow from the side of your hand. If the flame does not reappear, immediately turn the gas off and leave to cool because the barrel may be hot. Then light the Bunsen burner again.
26.6.6 Study the Bunsen burner flame
See diagram 3.2.1: Burning the gas in a cone of flame | See diagram 3.1.4.0: Bunsen burner flame | See diagram 3.2.0.0: Candle flame
1. Hold the end of a glass tube in the centre of the cone. You can light the gas coming out of the other end of the glass tube.
2. Hold a piece of wire in different parts of each kind of flame, moving it from the bottom to the top. Find the hottest flame and the hottest place in each flame with a piece of nichrome wire or iron wire stuck into a cork for a handle.
The approximate temperatures and colours for the wire are as follows:
2.1. < 500oC, wire gives no light, flame is non-luminous,
2.2. 500oC to 950oC, wire becomes red, then dark red, then bright red (red hot),
2.3. 950oC to 1350oC, wire becomes red- yellow then becomes white,
2.4. >1350oC, wire becomes white (white hot).
The safety flame has a similar temperature in different parts about 300oC. It is never used for heating. The medium blue flame has the hottest point at the tip of the blue cone at about 500oC. The roaring blue flame has the hottest point at the tip of the cone at about 700oC.
3. Close the air regulator. Use a wood splint or a taper to test that parts of the flame support ignition. The wood splint match is set alight in all positions in the yellow flame where no air mixes with the gas. Repeat the experiment with the air regulator open. A cone of mixed air and gas exists in the centre of the cone where the gas is not burning.
4. Turn off the gas. Push a pin at right angles through a match just below the chemical on the end of the match. Use the pin to hang the match in the barrel with the chemical end just above the rim. Open the air regulator and light the gas again. The match does not ignite inside the cone. Move the match to the outer cone of the blue flame. The match ignites.
5. Close the air regulator and light the gas. Hold a piece of copper wire gauze with tongs 3 cm above the top of the barrel. Hold a lighted match above the gauze. The gas ignites above the gauze. Lower the gauze until the flame passes through it. Repeat the experiment with an open air regulator. Light the gas and lower a copper wire gauze down on the flame. The flame remains below the wire gauze as the gauze becomes red hot. Heat is removed from the gas air mixture by the copper gauze.
6. Study a candle flame. Repeat the above experiments with a candle and a spirit burner. Just above the wick of a burning candle is a dark region of unburned gas. Above and around it is a yellow region containing incandescent particles of carbon undergoing combustion to form carbon dioxide. Put the candle flame under an evaporating basin. Note the deposits of carbon, soot, because of insufficient oxygen gas to complete combustion.
22.7.0 Thermometers, commercial thermometers
Thermometry, thermometers, temperature scale, upper and lower fixed points, mercury thermometer, alcohol thermometer, clinical thermometer, liquid crystal thermometer
See diagram 23.7.01: Science experiments thermometer | See diagram 23.7.02: Clinical thermometer | See diagram 23.7.03: Wall thermometer
A thermometer uses changes in a selected property to measure changes in temperature e.g. change of length in thermostats change in volume in mercury thermometers change in pressure in gas thermometers change in resistance of wires change in the emf in thermocouples. To calibrate a thermometer in oC the value of the selected property is first found at the ice point and mark this 0oC. Then the value of the property is found at the steam point and mark this 100oC. Divide the change in property between 0oC and 100oC into 100 equal parts each equivalent to a change in temperature of 1oC.
The International Temperature Scale (1990) extends from −272.5 °C to approximately 1,085 °C. Thermometers containing mercury are being phased out in schools. In hospitals mercury thermometers are being replaced by electronic digital thermometers, ear thermometers
22.7.01 Commercial thermometers
Thermometers, alcohol, -10oC to 110oC, 250 mm long
Thermometers, alcohol, -10oC to 110oC, 300 mm long
Thermometers, alcohol, -15oC to 50oC, classroom, wall, hanging type, not used in direct sunlight
Thermometer stand, wooden, holds 20 thermometers, fits 200 mm to 300 mm laboratory thermometers
Digital thermometer, indoor / outdoor, with minimum / maximum capacity, -50oC to 70oC
Digital fever thermometer, water resistant, speed read, display in Celsius, memory recall of last reading, includes 10 disposable probe covers, replaceable battery, medical accessory
Digital thermometer, Omron MC510 Gentle Temp electronic ear thermometer, LCD display, measures body temperature in 10 seconds, backlit screen, long life battery, compact, light weight
Probe covers for electronic ear thermometers
Clinical thermometer, mercury in glass, alcohol thermometer
Maximum and minimum thermometer, Six's thermometer, mercury in glass
22.7.02 Edited instructions for use of a "beurer" express-thermometer FT15
This thermometer is powered by an alkali manganese battery. This thermometer has a flexible measuring tip to provide greater comfort and safety during measurement, particularly in infants and persons who are asleep or have a reduced level of consciousness. Using the thermometer in strong electromagnetic fields such as next to a mobile phone, can cause a malfunction. Portable and mobile HF communication systems may interfere with this unit.
Temperature measurement in the anus (rectal) is the most reliable and most accurate method. Guide the tip of the thermometer carefully 2 to 3 cm into the anus. The measurement time with this thermometer at this site is only about 10 seconds. The end of the measuring time is indicated by an signal tone.
For measurement in the mouth cavity (oral measurement), guide the tip of the thermometer carefully into one of the heat pouches beneath the tongue, to the left or the right of the root of the tongue.
For measurement in the armpit (axillary measurement), this method of measurement is relatively inaccurate, so it cannot be recommended from a medical point of view.
Range of measurement: 32oC to 42.9oC
Accuracy of measurement: ± 0.1oC in a water bath with a temperature of 35.5oC to 42.0oC
Ambient temperature: 10oC to 40oC, with 30% to 85% relative humidity
22.7.1 Temperature sense, feeling "warm" and "cold", measure temperature correctly only with thermometer
1. Check if your temperature sense is reliable. Use containers of hot water, warm water and cold water. Put both hands in the warm water. The hands feel the same temperature. Put one hand in the hot water and the other hand in the cold water. Quickly dry your hands and put them both into the warm water again. The two hands do not feel the same temperature. This experiment shows that your temperature sense is not always reliable.
2. Fill three plastic dishes with the same amount of water but at different temperature 10oC, 20oC, 30oC. To get water at different temperature more accurate first pour some cold water then put heat water stir lightly with a spoon to make temperature evenly. Arrange three dishes from left to right with temperature from low to high. Let two students one put his right hand into 10oC water the other put his left hand into 30oC water. After two minutes take out their hands at the same time swing strength then put hands into dish at 20oC in the middle simultaneously in time. Let each student say the water in the middle dish is warm or cold. The experiment shows that you can judge if an object is warm or cold by your sensation. However, this method is limited to a qualitative judge shows more relatively the degree of warm and cold of an object. The objects which have the same degree of warm or cold can be judged to a different conclusion of degree of warm or cold under different cases. You feel warmer as your hand removes from water in lower temperature to that of higher temperature while you feel colder as your hand removes from water in higher temperature to that of lower temperature. As you can see warm and cold have not a definite standard. This cannot meet the needs of showing degree of warm and cold scientifically. To show the degree of warm and cold of an object quantitatively it is necessary to introduce an important quantity, temperature and make an equipment which can measure the temperature, the thermometer.
22.7.2 Expansion of liquid in a thermometer
1. Fill a flask with coloured water. Insert a one hole stopper carrying a 30 cm length of glass tubing until the water rises 5 cm in the tubing. Put the flask in a beaker of water. Heat the beaker and observe the water level in the tubing. The water rises in the tubing. However, if you carefully observe the water level in the tubing when the heating begins, you will see that it falls slightly and then begins to rise! It falls because the glass in the flask starts to expand before the water inside. When the heat energy reaches the water it expands. So the expansion of liquid you see in a thermometer is really the expansion of liquid less the expansion of the glass tube.
2. Put some crushed ice in a Erlenmeyer flask add a little water. The depth of mixture in the flask is about one inch. Spin the flask to mix water and ice. Insert a thermometer into the mixture. As the column of liquid in thermometer is stable mark on thermometer beside the scale marked 0oC. Put the flask on wire gauze on a tripod heat it with a burner. As water in the flask boils mark again as 100oC. Note to maintain two marks at the same vertical line. The freezing and boiling point of water are primary standards for calibrating thermometer. Draw a scale of thermometer between 0oC and 100oC. Divide it into 100 same spaces. Draw a longer line every 10 points written as 10oC, 20oC ... Draw a shorter line every 5 points written as 5oC, 15oC, 25oC... Compare the scale you have done to original one. Perhaps they are quite different. The main reason is the scale lines of 100oC are not the same because the atmospheric pressure is not the standard as you do the experiment and the boiling point of water may not exactly the 100oC. To draw line and calibrate easily you can use a sheet of coordinate paper stuck to the thermometer in advance.
22.7.3 Thermometer test, calibrate a thermometer
There are two marked points on the scale of a thermometer. If a thermometer can measure the temperature from 0oC to 100oC the two fixed points are at 0oC and 100oC. 0oC is the melting point of ice and 100oC is the boiling point of water. Other scales of temperature are all defined refer to two fixed points. The melting point and boiling point depend on atmospheric pressure so the melting point of ice and the boiling point of water are at standard atmosphere.
1. Use a thermometer with a scale, e.g. thermometer -10oC to 110oC mercury or alcohol, or a tall flask containing coloured water fitted with a one hole stopper and glass tube that extends into the bottle. Mark thermometer scales at two fixed points. The lower fixed point is the temperature of melting ice. Put the bulb of a thermometer in crushed ice that is melting. Leave it there for some minutes. Check that the temperature is 0oC on the calibrated thermometer, or make a mark on the blank scale or on the glass tube attached to the small flask. The upper fixed point is the temperature of boiling water. Put a thermometer in steam immediately above the surface of boiling water. Leave it there for some minutes. Check that the thermometer reads 100oC on the calibrated thermometer, or make a mark on the blank scale or on the glass tube attached to the small flask. Divide the distance between the upper and lower fixed point to obtain marks representing a temperature difference of 1oC. If you do the experiment on a mountain at high altitudes the temperature of boiling water may be below 100oC because of the reduced atmospheric pressure. If you do the experiment in a submerged submarine the temperature of boiling water may be above 100oC. The thermometer in the boiling water reads exactly 100oC only at sea level or where the barometer reading is 760 mm of mercury.
22.7.4 Thermometer, 0oC to 100oC range
First put thermometer into crushed ice after a few minutes observe if the liquid column in the thermometer is exactly at 0oC. Take out the thermometer from the ice wait for a while at the temperature of surroundings. Put the thermometer on the surface of boiling water the measuring bulb is near the heat steam above the surface of water. Wait for a few minutes observe if the liquid column in the thermometer is at the scale of 100oC. Note if you live in the region of higher height above sea level the boiling point of water there will be lower than 100oC due to the lower atmospheric pressure. On the contrary in the region of lower height above sea level the boiling point of water will be higher than 100oC. Only in height of sea level the boiling point of water is just 100oC the atmospheric pressure there is 760 mm Hg.
22.7.5 Thermometer, make a thermometer
Prepare a small glass bottle with a rubber stopper which is punched a hole and installed a thin glass tube long enough. This is a thermometer the small bottle is a measuring bulb the thin glass tube is a pole. Pour a few drops of red ink in the water close the stopper to make no air inside the bottle. The glass tube must be sealed by stopper as tightly as possible until surface of water cannot rise up. Mark 0oC and 100oC according to the steps above. If it is not possible to measure 0oC and 100oC because of the limit of level of water and size of tube, you can select two suitable temperature points by yourself. However, this time you must find the temperature by means of a accurate thermometer. Measure the length between 0oC to 100oC on the glass tube divide the length into 10 evenly and mark on the wall of the tube. (i.e. mark 9 points in same distance each other between 0oC to 100oC). Write 10oC to 90oC in turn, i.e. every space is 10oC. You may divide by 10 again between every space and mark it. This time every space is 1oC. So a thermometer is finished. If you live in the region of higher height above sea level correct the fixed point of 100oC according to the boiling temperature there.
22.7.6 Thermocouple, thermistor, constantan, optical pyrometer
A thermocouple has two different wires or semiconductors joined at the ends to be a thermoelectric source of EMF, Seebeck effect, when the wires are at different temperatures. It is used to detect very small differences in temperatures. For more sensitivity, thermocouples are joined in series to make a thermopile, pile.
Thermistors are wires used in electronic circuits made of metal oxides that decrease in resistance when the temperature of the wire increases.
Constantan is an alloy, about 40% nickel and 60% copper, having high volume resistivity and negligible temperature coefficient. So resistance hardly changes with change in temperature. It is used for resistance wire, also Eureka wire. CrAl (Kranthal) and NiCrm (Nichrome wire) have very high resistivity. An optical pyrometer is used to measure very high temperatures from the colour of the radiant heat source.
1. Attach a piece of copper and a piece of constantan to two wires. Heat lead to above its boiling point of 327oC. Attach the wires to a galvanometer and insert the copper and constantan into the boiling lead. The galvanometer can be calibrated to read temperature and act as a thermocouple to read the temperature of the molten lead.
22.7.7 Galileo's thermometer
Use a set of glass spheroid buoys of varying density in a glass cylinder arranged so the lowest floating ball represents the temperature.
22.7.8 Air thermometer
See diagram 23.4.9
Select a small medicine bottle with a cork stopper. Bore a hole through the cork with a cork borer to take a piece of thin glass tubing 30 cm long. Put ink in the bottle to cover the end of the tubing, which should be touching the bottom of the bottle. Warm the bottle with your hands to make the air in the bottle expand, press down on the liquid in the bottle and force it up the glass tube.
22.5.0 Specific heat capacity, shc
Specific heat capacity is the heat required to raise the temperature of the unit mass of a given substance by a given amount, e.g. 1oC, under specified conditions.
1. The amount of heat absorbed by object per unit of mass as the temperature rises is called the specific heat capacity, symbol "c" or "shc". Specific heat is usually measured as the amount of heat required to raise the temperature of 1 kilogram of the substance by 1oC. Its unit is joule / kgoC. For water, shc = 4200 joule / kgoC (or 4.1813 J g-1K-1 at 25oC). For copper, shc = 385 joule / kgoC, [385 J / (kg K)]. These values are the same if specific heat capacity is expressed using the Celsius scale or the Kelvin scale because the one degree interval has the same magnitude on each scale.
2. The heat required to raise the temperature of 15 kg mass of copper from 15oC to 25oC = mass × (t2 -t1) × specific heat = 15 kg × (25 - 15)oC × 380 joule / kgoC = 15 × 10 × 380 = 57000 joule, J (j).
3. Specific heat is the character of the material itself. The c values of a substance may be different in different states. The c values of the same gases are quoted as specific heat at constant volume (cv) for when only its internal energy is increased, or specific heat at constant pressure (cp), which requires more heat because the gas expands. For solids and liquids, the difference between specific heat values is very small.
4. Specific heat capacity is the ratio of the thermal capacity of the substance to the thermal capacity of water at 15oC so is numerically equal to heat capacity (thermal capacity) with the SI unit J kg-1oC-1.
22.5.01 Specific heat of water
Note the very high and unexplained specific heat of water, 4.1823 J g-1 K-1, (4.2 joules per gram per kelvin) at 25oC. The higher specific heat means that water is very suitable for use in central heating systems or cooling engines. Water has about five times the specific heat capacity of land keeping islands cooler in summer and hotter in winter. So continents have greater temperature variations than islands. The exceptionally high heat capacity of water slow temperature changes, allows heat to be transported around the world by ocean currents and influences climate change.
22.5.02 Molar heat capacity, Cm
1. Dulong and Petit's law states that relative atomic mass × specific heat = constant, approximately 25 J mol-1K-1
Molar heat capacity of a solid element, Cm = relative atomic mass × specific heat capacity = approximately 25 J mol-1K-1 (6.0 cal mol-1K-1) = 3R (where R = universal gas constant 8.314 J mol-1K-1) [3X 8.314 = 24.942]
If specific heat is expressed as gram heat capacity expressed as J g-1K-1, and specific heat of iron = 0.473 J g-1K-1, then the ratio: molar heat capacity / specific heat = 25 J mol-1K-1 / 0.473 J g-1K-1 = 52 .85 = approximately 55.847, the molar mass of iron. The molar heat capacity of non-metal compounds ot metallic salts is about 60-80% of the molar capacity of heavy metals.
22.5.03 Heat capacity (thermal capacity) C, of a calorimeter
Heat capacity (thermal capacity) is the capacity of a body to store heat and is measured by the quantity of heat required to raise its temperature by one degree. The SI unit is J kg-1oC-1.
A calorimeter is an insulated vessel usually containing water and used to measure the thermal quantities of a process, heat changes.
Heat capacity, Cp, is the ratio: heat given to an object / rise in temperature of the object and is expressed in joules per kelvin, J K-1. The heat capacity of the calorimeter itself is usually measured as the amount of heat needed to raise the temperature of the calorimeter by 1 K. This value is usually found by experiment that involves transferring a known amount of heat into it and measuring its temperature increase. This experiment is done before measuring the heat capacity of an unknown substance. For example if the temperature of a calorimeter increases by 0.2 K when 8.0 J of electrical energy is used to heat it, the heat capacity of the calorimeter, C = 8 .0 / 0.15 = 53.3 J / K.
The heat capacity of the calorimeter is usually compared with the heat capacity of an amount of water.
The heat capacity of one mole of water, Cp,m = 18 g mol-1 × 1 cal g-1K-1 × 4.184 J cal-1 = 75.312 J mol-1K-1at 25oC.
22.5.1 Melting wax calorimeter
See diagram 24.1.1: Melting wax calorimeter
Prepare equal masses of aluminium, steel and lead. Tie a thread to each metal and put each into a copper beaker. Pour the same volume of boiling water on the metals. Use a smooth wooden board. Its size can meet the needs of all metals arranged one by one leaving space between each. Cover a thick layer of paraffin wax evenly on the board in advance. Lift the thread tied to the metal out of the boiling water, put it rapidly on the board. The hot metal produces a concavity on the layer of paraffin wax. After the paraffin wax stops melting, compare the width and depth of different concavities that can show that different metal has different specific heat. From this you can know roughly the values of specific heat of different metals.
22.5.2 Specific heat of water by electrical method
1. Examine the electric jug or immersion heater for a power rating in watts. If power is not shown on an immersion heater, put immersion heater in water, connect to its power supply with an ammeter in the circuit, e.g. 12 volts DC. and note current used, e.g. 4 amps. power, P = VI = volts × amps = 12 × 4 = 48 watts. You can also use an ohmmeter to measure the resistance of the heating element and find the current drawn by the element using Ohm's Law, V = IR. Then calculate the power rating of the element.
2. Measure 1 litre of water. The heating element must be completely immersed in the water.
3. Measure the temperature of the water, t1
4. Switch on the electric power and record the time.
5. After a period of time when the temperature of the water has increased but before the water boils, i.e. below 100oC, switch off the power and record the time and the temperature of the water, t2.
6. Q = mc(t2 - t1), where Q is the energy absorbed, m is the mass of the water, "c" is the specific heat of water and t1 and t2 are the initial and final temperatures of the water. Assume that the water absorbs all of the energy output from the heating element. Thus, P = Q / t where P is the power rating of the element, t is the time taken to heat the water. Therefore, P = mc(t2 - t1) / t. Specific heat of water, c = 4186 J / kgoC.
If a 3 kW immersion heater raises the temperature of 60 kg water from 10oC to 60oC in 70 minutes.
Heat from immersion heater = heat gained by water.
3000 joules × 70 × 60 seconds = 60 kg × c × (60 -10)oC,
c = 4200 J / kgoC
22.5.2.1 Specific heat of aluminium by electrical method
1. Use a solid aluminium cylinder with 2 holes drilled into it and weighing 1 kg. Put a thermometer in one hole and an electric immersion heater, e.g. 12 V power supply, into the other hole. Record temperature when steady and time taken. Power of immersion heater, J × time immersion heater switched on, seconds, s = mass, m (1 Kg) × c × (t2 -t1).
2. Connect an immersion heater to the 12 volt supply in series with an ammeter and a rheostat. The immersion heaters are 12 volt, 60 watts. Adjust the rheostat to a current of about 4 amps. Insert the immersion heater in the aluminium block and the thermometer in its hole in the block. Use paraffin oil in the thermometer hole to ensure good thermal contact with the block. Wait for five minutes then record the temperature of the block. Close the switch. Start the clock and note the temperature change. Take the temperature every half minute and draw a graph. Connect the immersion heater to the 12 volt supply in series with an ammeter and a rheostat. The immersion heaters are 12 volt, 60 watts. Adjust the rheostat to give a current of about 4 amps. Switch on, start the clock and note the temperature change. Two methods can be used: 1. Take the temperature every half minute and plot a graph. 2. Take the total temperature rise over the known heating period. Continue recording temperature after the switch is opened. If the potential difference across the heater gave a current through it of 31 amps, and the temperature rose from 24.5oC to 37.8oC in six minutes when the electricity supply was turned off, the temperature may continue to rise to 40.1oC after 8.5 minutes. Close the switch, start the clock, record the temperature, open the switch after 10oC rise, record the time for which the heater was in operation, record the temperature after a further four minutes has elapsed. (temperature rise, oC × specific heat) / time, seconds = (current, amps × potential difference, volts) / J.
22.5.3 Heat capacity (water equivalent)
The heat capacity (water equivalent) of a body is the quantity of heat the body absorbs when its temperature is raised through one degree Celsius. This quantity may also be defined as as the mass of water that requires the same quantity of heat energy to raise its temperature through one degree Celsius as the body itself requires. So the water equivalent of 1 kg of iron is 1 kg. If m = mass of the body, and s = specific heat of the material in the body, then heat capacity, (water equivalent) = ms.
The heat capacity of water at 100oC is 4.22 J / gK
Put 1 litre of water in a beaker and 1 kg aluminium + water in another beaker and heat on the same hot plate then measure the temperature in each beaker. Heat two beakers one with 1 Kg water and the other with 5 Kg water and 5 Kg lead at the same rate. Heat two beakers on a single hot plate each contains the same mass of either water or oil, water and oil. Heat an iron plate and a beaker of water with the same mass on identical Bunsen burners then dip your hand in the water and sprinkle it on the iron plate where it will sizzle.
22.5.4 Mix heated water
Mix different masses of hot and cold water and compare the final temperature to the calculated value. If the temperature of a 10 kg mass of copper, specific heat capacity 400 J / kgoC, rises from 20oC to 35oC, heat received by copper mass: H = mc(t2-t1) = 10 × 400 × (35 -20) = 60, 000 joules, J.
22.5.5 Specific heat calorimeter
Heat known masses of lead and copper are heated and put into calorimeters with a known mass of water then calculate specific heats of metals from initial and final temperatures.
If 1 kg aluminium in boiling water (100oC) put in 0.5 kg water at 10oC and temperature of water rises to 38.23oC.
Specific heat of water =4200 J / kgoC
Heat lost by aluminium = mass × specific heat × (final temperature - initial temperature) = 1 × c × (100 -38.23)
Heat gained by water = mass × specific heat × (final temperature - initial temperature) = 0.5 × 4200 × (38.23 -10)
heat lost = heat gained, so 1 × c × 61.77 = 2100 × 28.23, c = 959.7 J / kgoC (specific heat of aluminium = 960 J / kgoC)
23.5.6 Heat capacity of a metal with a Styrofoam cup calorimeter
A calorimeter made from two Styrofoam coffee cups is a constant pressure calorimeter in that measures the change in enthalpy of a reaction with the atmospheric pressure remaining constant.
Cp = [W × dH / (M × dT)], where dH = enthalpy of solution, dT = change of temperature, w = weight of solute, m = molecular weight of solute
In calorimetry, dH is the heat energy released at constant pressure and dE is the energy released at constant volume. dH = dE + [d(PV)], where
The enthalpy increase, dH, is the heat added to a system at constant pressure.
dH = mCpdT
where dH = change in enthalpy, m = mass of substance, Cp = heat capacity at constant pressure (J g-1K-1), dT = temperature change.
Styrofoam cup + cool water + hot water = 0
dHcal + dHcw + dHhw = 0
mCpdT + mcwCpdTcw + mhwCpdThw = 0
Let B, the calorimeter constant for the Styrofoam cup = MCp J /K
The calorimeter constant describes how the calorimeter responds to added heat.
So BdTcw + mcwCpdTcw + mhwCpdThw = 0
1. Measure the calorimeter constant, B
Use two Styrofoam cups, one inside the other, as a calorimeter. Weigh the two Styrofoam cups empty, m1, add 70 mL of water at room temperature and weigh the two Styrofoam cups again, m1 + 70, and record the temperature of the water in the calorimeter, T1. Boil water in a beaker, record the temperature, T2, and pour 30 mL of the boiling water into the calorimeter. Be careful! Gently stir the water with a thermometer with the bulb 3 cm above the bottom and record the highest temperature, T3 and mass M1 + 100.
B × (T3 - T1) + 70 × (T3 - T1) + 70 × (100 - T3) = 0
2. Measure the heat capacity of a metal, e.g. lead shot
Put a a test-tube containing lead shot in boiling water. Repeat the above experiment but add the hot lead shot to the calorimeter instead of the 30 mL of boiling water.
B × (T3 - T1) + 70 × (T3 - T1) + 70 × (100 - T3) = 0
3. The heat capacity of a metal in joules per gram per kelvin × molar mass of the metal in grams per mole = the constant, Cp × M = 25 J mol-1 K-1 (Dulong and Petit's law)
Heat capacity of metals expressed as joules per gram per degree Kelvin, J.g-1.K-1
Mg 1.04, Al 0.904, Fe 0.473, Ni 0.444, Cu 0.387, Zn 0.386, Ag 0.236, Sb 0.207, Au 0.129, Pb 0.128
22.5.6 Ice calorimeter
Heat different metals of the same mass to the same temp and lower into funnels filled with crushed ice then collect the melted water in graduated cylinders.
22.5.7 Heat of combustion, bomb calorimeter
See diagram 23.5.7: Bomb calorimeter
See 6.6.17 Bomb calorimeter, Energy from food, bomb calorimeter
Use a bomb calorimeter to show heating value of foods and fuel.
dH = heat energy released at constant pressure, dE = heat energy released at constant volume, dH = dE + [d(PV)] = dE + dn RT (from ideal gas laws)
Measuring heat produced at constant volume, qv, = C dT (temperature change)
here qv = change in internal energy dE, so dE = qv = CdT
The heat capacity of a calorimeter can be calculated by burning a known weight of a standard substance, e.g. benzoic acid, dH = -3227 kJ mol-1.
22.5.8 Candle burns below water level
Cut a candle to be slightly longer than the depth of a large beaker. Melt the base of the cut candle and fix it to the base of the beaker. Fill the beaker with water up to the rim of the candle. Light the candle and observe it burning down to below the level of the water as it forms a wax wall around the flame. Water has a high heat capacity that allows it to absorb heat from the candle wax so it does not melt and evaporate but instead form a wall around the flame.
22.10.0 Mechanical equivalent of heat, Joule's equivalent
Before SI units were adopted, Joule's equivalent, (James Prescott Joule 1818-1889), was the conversion coefficient between mechanical work and heat. 4.186 J = 1 calorie, i.e. J = 4.2 joules per calorie. A typical experiment was to stir water with a paddle moved by a falling mass. For example, a 1000 g mass falling 83.8 metres rotates a paddle in a calorimeter (paddle + calorimeter = 250g), specific heat 0.10, causes a rise in temperature of 0.28oC. Loss of energy by falling mass = mgh = 1000 × 980 × 8380 ergs = 8.21 × 109 ergs. Heat taken in by calorimeter and paddle = mass × specific heat × change in temperature = mst = (250 × 0.10 × 0.28) = 7 calories, + heat taken in by water = mst = (675 × 1 × 0.28) = 189 calories. So total heat taken in = 7 + 189 = 196 calories. W = JH, 8.21 × 109 = J × 196, so J = 4.19 × 107 ergs per calorie = 4.2 joules per calorie.
However, in SI units all forms of energy are expressed in joules, so J =1, and the specific heat capacity of water = 4.186 (4.2) kJkg-1K-1.
(heat capacity = joules per kelvin, specific heat capacity = joules per kilogram per kelvin).
22.10.1 Waterfall
If 10 kg water falls 150 metres and all the energy converted to heat (silent waterfall!), and g = 9.8 m / s2
potential energy of water = mgh = 10 × 9.8 × 150 = 14700 joule, J
H = mc(t2-t1), where c = 4200 J / kgoC = 10 × 4200 × (t2 - t1)
14700 = 42000 (t2-t1), so difference in temperature (t2 -t1) = 14700 / 42000 = 0.35oC.
22.10.2 Dropping lead shot
1. Record the temperature inside a bag containing 1 kg of lead shot. Drop the bag of lead shot from a height of 2 metres 20 times in quick succession. Record the temperature inside the bag.
2. Put 1 kg of lead shot in a mailing tube, cardboard cylinder, invert 10 times and measure the rise in temperature rise.
22.10.3 Hammer on lead
Hit a lead block with a heavy hammer and measure the temperature rise.
22.10.4 Heat by bending
Keep bending an iron wire and measure the rise in temperature.
22.10.5 Friction ignition, bow and stick, fire maker, drill and dowel
Make a fire with a bow and stick. Hold an electric drill with a hardwood dowel in the chuck against a wood block.
22.10.6 Flint and steel
Make sparks fly from flint rubbing against steel or a grindstone.
22.10.7 Mechanical equivalent of heat, J, by an electrical method
See diagram 32.2.64
The heat energy expended by a current of I amps flowing under a potential difference V volts for t seconds = VIt / J, where J = a constant called the mechanical equivalent of heat. If heat lost from the calorimeter to the surroundings is small, the heat energy supplied by the coil = heat energy received by the calorimeter + contents. Weigh the calorimeter + stirrer, m1. Weigh the calorimeter + stirrer + enough water to cover the heating coil, m2. Adjust the rheostat or power supply to a current of 3 amps. Open the switch, stir the water and note the initial temperature T1oC. Close the switch and record the time. Record the current I amps through the coil. Record the potential difference V volts across the coil. Allow the current to flow, still stirring, until the water temperature has risen 10oC. Open the switch and record the highest steady temperature, T2oC. Record the time of flow of the current, t seconds. The specific heat of water = 4.2 kg-1K-1 (or oC). The specific heat calorimeter and stirrer, usually copper = s. Calculate J using the following equation: Heat energy supplied = heat received by water + heat received by calorimeter and stirrer. VIt / J = ([m2 -m1]swater [T2 - T1]) + (m1 × s × [T2 -T1]).