GEK Wiki / Properties of Air
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Properties of Air

Page history last edited by jim mason 14 years, 12 months ago

Components in Dry Air

 

The two most dominant components in dry air are Oxygen and Nitrogen. Oxygen has a 16 atomic unit mass and Nitrogen has a 14 atomic units mass. Since both of these elements are diatomic in air - O2 and N2, the molecular mass of Oxygen is 32 and the molecular mass of Nitrogen is 28.

 

Air is a mixture of gases and the total mass can be estimated by adding the weight of all major components as shown here:

 

Components in Dry Air

Volume Ratio in Dry Air

Mass Ratio in Dry Air

Molecular Mass - M
(kg/kmol)
Molecular Mass in Air
Oxygen 0.2095 .2320 32.00 6.704
Nitrogen 0.7809 .7547 28.02 21.88
Carbon Dioxide 0.0003 .00046 44.01 0.013
Hydrogen 0.0000005   2.02 0
Argon 0.00933 .0128 39.94 0.373
Neon 0.000018   20.18 0
Helium 0.000005   4.00 0
Krypton 0.000001   83.8 0
Xenon 9E-6   131.29 0
Total Molecular Mass of Air   28.97

(from engineeringtoolbox http://www.engineeringtoolbox.com/molecular-mass-air-d_679.html)

 

The "Mass Ratio" is useful for combustion calculations (e.g. to get 1kg of oxygen, we need 1/0.2320 = 4.31kg of air).

 

Additional Resources:

Air Property Calculator

 

 

Under standard conditions (25oC, 1atm), the density of air is about 1.168kgm-3.

Hence 1kg of air would have a volume of:

1kg/1.168kgm-3

= 0.8562m3

 

 

 

 

 

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