Gas Mixture Properties

Special care must be taken for gas mixtures when using the ideal gas law, calculating the mass, the individual gas constant or the density

Mixture of gases are common in many applications. Our most common example is air - mainly consisting of nitrogen, oxygen and water vapor - moist air. Combustion gas, mainly consisting of nitrogen, water vapor and carbon dioxide, is an other example.

Special care must be taken for gas mixtures when using the ideal gas law, calculating the mass, the individual gas constant or the density.

The Ideal Gas Law for a Gas Mixture

The Ideal Gas Law for a perfect or ideal gas adapted for a gas mixture:

pV = m_mG_mT         (1)

where

p = absolute pressure in the mixture (N/m², lb/ft²)

V = volume of the mixture(m³, ft³)

m_m = mass of the mixture (kg, lb)

G = the individual gas constant for the mixture (J/kg K, ft lb/slugs ^oR)

T = absolute temperature in the mixture (^oK, ^oR)

The Mass of the Gas Mixture

The mass of the mixture can be expresses as:

m_m = m₁ + m₂ +..+ m_n         (2)

where

m₁ + m₂ +..+ m_n = the mass of each gas component in the mixture

The Individual Gas Constant of the Gas Mixture

The individual gas constant for the gas mixture can be expressed as:

G_m = (G₁m₁+ G₂m₂ +..+ G_nm_n) / (m₁ + m₂ +..+ m_n )         (3)

The Density of the Gas Mixture

The density of a gas mixture can be calculated as:

ρ_m = (ρ₁v₁ + ρ₂v₂ + .. + ρ_nv_n)/(v₁ + v₂ + .. + v_n )         (4)

where

ρ_m = density of the gas mixture (kg/m³, lb/ft³)

ρ_{1 ..} ρ_n = density of each of the components (kg/m³, lb/ft³)

v₁ + v₂ + .. + v_n = volume share of each of the components (m³, ft³)

• Density, Specific Weight and Specific Gravity

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