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

See Also

• Ideal gas law