School Science Lessons
2012-04-24 SP
Please send comments to: J.Elfick@uq.edu.au
1.0.0 SVP, Saturation Vapour Pressure
NTP, Normal Temperature and Pressure is air at 20oC (293.15 K and 1 atm (101.325 kN / m2,
101.325 kPa, 30 inches Hg, 760 torr)
NTP dry air has a density of 1.204 kg / m3.
STP, Standard Temperature and Pressure is air at 0oC (273.15 K, and 1 atm (101.325 kN / m2,
101.325 kPa, 30 inches Hg, 760 torr)
STP dry air has a density of 1.275 kg / m3.
Standard sea level atmospheric pressure = 101 325 Pa
Air density, Kg / m3 = [1.2929 × 273.13 × (AP - ( SVP × RH ) / ( T + 273.13)] × 760
Where:
T = oC
AP = Absolute Pressure, mm of Hg
SVP = Saturation Vapour Pressure of air over water at temp T
RH = Relative Humidity (decimal)
High air density readings indicate more oxygen in the air.
Gas Formula Molecular weight Density, NTP,
kg / m3		 Density, STP,
kg / m3
Air . 29 1.2041 1.2929
Ammonia NH3 17.031 0.717 0.769
Argon Ar 39.948 1.661 1.7837
n-Butane C4H10 58.1 2.4891 2.672
Carbon dioxide CO2 44.01 1.842 1.977
Carbon monoxide CO 28.01 1.165 1.250
Chlorine Cl2 70.906 2.994 4.214
Ethane C2H6 30.07 1.264 1.356
Ethene (ethylene) C2H4 28.03 . 1.260
Ethyne (acetylene)
 C2H2 26 1.092 1.173
Helium He 4.02 0.1664 0.1785
Hydrogen H2 2.016 . 0.0899
Hydrogen chloride HCl 36.5 1.528 1.639
Hydrogen sulfide H2S 34.076 1.434 1.538
Methane CH4 16.043 0.668 0.717
Natural gas . 19.5 . 0.862
Neon Ne 20.179 . 0.902
Nitric oxide NO 30.0 1.249 1.389
Nitrogen N2 28.02 1.165 1.2506
Nitrogen dioxide NO2 46.006 . .
Nitrous oxide N2O 44.013 .
 1.978
Oxygen O2 32 1.331 1.4290
Ozone O3 48.0 . .
Propane C3H8 44.09 1.882 2.019
Propene (propylene) C3H6 42.1 1.748 .
Sulfur dioxide SO2 64.06 2.279 2.927
Water vapour H2O 18.016 0.804 .

Saturation vapour pressure over water
oC kPa oC kPa oC kPa oC kPa oC kPa
0 0.611 .
 .
 .
 .
 .
 .
 .
 .
1 0.657 11
 1.312 21
 2.487 31
 4.495 41
 7.382
2 0.706 12
 1.402 22
 2.644 32
 4.758 42
 8.206
3 0.758 13
 1.497 23
 2.810 33
 5.033 43
 8.647
4 0.813 14
 1.598 24
 2.985
 34
 5.323 44
 9.109
5 0.872 15
 1.705 25
 3.169
 35
 5.627 45
 9.591
6 0.935 16
 1.818 26
 3.362 36
 5.945 46
 10.095
7 1.002 17
 1.938 27
 3.567 37
 6.280 47
 10.622
8 1.073 18
 2.064 28
 3.781 38
 6.630 48
 11.173
9 1.148 19
 2.197 29
 4.007 39
 6.997 49
 11.747
10
 1.228 20
 2.338 30
 4.245 40
 7.382 50
 12.347