# Air

Air is hopefully self-explanatory. It is one of the most basic and essential words in any language. The speed of sound in dry air at 20°C and 1atm is 343m/s.

## Composition

Components of air
1 liter 1 m3
moles grams moles grams
1atm, 20°C, 0% humidity
Nitrogen (N2) 0.0324 0.9072 32.4 907.2
Oxygen (O2) 0.0087 0.2784 8.7 278.4
Argon (Ar) 0.0004 0.016 0.3984 16
Carbon Dioxide (CO2) 0.0000166 0.0007304 0.0166 0.7304
Check(sum) 0.0415✓ 1.2017✓ 41.515✓ 1201.7✓
1 atm, 20°C, 100% humidity
Water (H2O) 0.0009 0.0162 0.9 16.2

Air is composed of 78% nitrogen, 21% oxygen, 0.96% argon and 0.04% carbon dioxide.

• Volume of 1 mol of a gas at 20°C: 24.05L
PV = nRT
V = nRT
P
P = 1 (atm)
n = 1 (mol)
R = 0.082057 (L atm K−1 mol-1) ideal gas constant
= 0.082057T
= 0.082057×293 = 24.042701
• Molar mass of air: 28.9776g/mol
= 0.78 * 28 + 0.21 * 32 + 0.01 * 40 + 0.0004 * 44
= 21.84 + 6.72 + 0.4 + .0176
= 28.9776
• Density of air: 1.20488 g/L (20°C, 1atm)
Density = g
L
(water = 1000)
= 28.9776g/mol
24.05L/mol
= 1.20488g/L at 20°C
• How many liters of air at 20°C represents 1mol of O2? 127L
1 mol of O2 weighs 32g (2x molar weight of oxygen)
Air is 21% O2 by mass
32g / 0.21 = 152g of air contains 32g (1 mol) of O2
152g
1.2g/L
= 127L of air at 20°C contains 1mol of O2
• Inversely, How many mol of O2 are in 1L of air? .0079
1/127 = .0079