Gas Mixtures - Properties
Mixture of gases are common in many applications. Our most common example is air - mainly consisting of nitrogen, oxygen and water vapor - as moist air. A combustion gas with 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:
p V = mm Rm T (1)
where
p = absolute pressure in the mixture (N/m2, lb/ft2)
V = volume of the mixture(m3, ft3)
mm = mass of the mixture (kg, lb)
Rm = 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 a Gas Mixture
The mass of a gas mixture can be expressed as:
mm = m1 + m2 + .. + mn (2)
where
m1 + m2 + .. + mn = the mass of each gas component in the mixture
The Individual Gas Constant of a Gas Mixture
The individual gas constant of a gas mixture can be calculated as:
Rm = (R1 m1 + R2 m2 + .. + Rn mn) / (m1 + m2 + .. + mn ) (3)
The Density of a Gas Mixture
The density of a gas mixture can be calculated as:
ρm = (ρ1 v1 +ρ2 v2 + .. + ρn vn) / (v1 + v2 + .. + vn ) (4)
where
ρm = density of the gas mixture (kg/m3, lb/ft3)
ρ1 .. ρn = density of each of the components (kg/m3, lb/ft3)
v1 + v2 + .. + vn = volume share of each of the components (m3, ft3)
Related Topics
• Fluid Mechanics
The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.
• Gases and Compressed Air
Properties of air, LNG, LPG and other common gases. Pipeline capacities and sizing of relief valves.
Related Documents
Air - Molecular Weight and Composition
Dry air is a mixture of gases where the average molecular weight (or molar mass) can be calculated by adding the weight of each component.
Helium - Thermophysical Properties
Chemical, Physical and Thermal Properties of Helium - He.
Non-ideal gas - Van der Waal's Equation and Constants
The van der Waals constants for more than 200 gases used to correct for non-ideal behavior of gases caused by intermolecular forces and the volume occupied by the gas particles.
The Ideal Gas Law
The relationship between volume, pressure, temperature and quantity of a gas, including definition of gas density.
Total and Partial Pressure - Dalton's Law of Partial Pressures
How to calculate total pressure and partial pressures for gas mixtures from Ideal Gas Law.
Universal and Individual Gas Constants
The Universal and Individual Gas Constants in fluid mechanics and thermodynamics. Individual gas constants for the most common gases.