Specific gas constant

The specific gas constant of a gas is given by the universal gas constant, divided by the molar mass of the gas.

Definition

Let:

$R\$be the universal gas constant, or about $8.314472{\frac {J}{molK}}\$

$r\$be the specific gas constant for the gas you are working with

$M\$be the molar mass of the gas

So then:

$r={\frac {R}{M}}\$ -or rewritten as- $R=rM\$

Examples

Helium

The molar mass of helium is:

$4.003{\frac {g}{mol}}$

Therefore, the specific gas constant of helium is:

${\frac {8.314472{\frac {J}{mol^{\circ }K}}}{4.003{\frac {g}{mol}}}}\approx 2.077{\frac {J}{g^{\circ }K}}\$

Air

The generally accepted molar mass of air is:

$28.97{\frac {g}{mol}}$

Therefore, the specific gas constant of air is:

${\frac {8.314472{\frac {J}{mol^{\circ }K}}}{28.97{\frac {g}{mol}}}}\approx .287{\frac {J}{g^{\circ }K}}\$