GEK Wiki / Properties of Air
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Properties of Air

Page history last edited by jim mason 11 years, 7 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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