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# Gas Mixtures - Properties

## Gas mixtures and the ideal gas law, mass calculations, the individual gas constant and density.

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

Air, LNG, LPG and other common gas properties, pipeline capacities, 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.

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## Citation

• The Engineering ToolBox (2004). Gas Mixtures - Properties. [online] Available at: https://www.engineeringtoolbox.com/gas-mixture-properties-d_586.html [Accessed Day Month Year].

Modify the access date according your visit.

9.19.12