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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