The Universal Gas Constant - R u - appears in the ideal gas law and can be expressed as the product between the Individual Gas Constant - R - for the particular gas - and the Molecular Weight - M gas - for the gas, and is the same for all ideal or perfect gases :
R u = M gas R 
The universal gas constant can be defined in terms of Boltzmann's constant k as:
R u = k N A 
k = Boltzmann's constant = 1.381 x 10 -23 [J/K]
N A = Avogadro Number = 6.022 x 10 23 [1/mol]
The average molecular weight of a gas mixture is equal to the sum of the mole fractions of each gas multiplied by the molecular weight of that particular gas:
M mixture = Σx i *M i = (x 1 *M 1 + ......+ x n *M n ) 
x i = mole fractions of each gas
M i = the molar mass of each gas
- More material properties
- The Ideal Gas Law - Gases are highly compressible with changes in density directly related to changes in temperature and pressure.
- A Mixture of Gases - Properties of mixtures of gases.
- More about temperature
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