Formula Definition of the Specific Gas Constant Molar mass
$$R_{\text s} ~=~ \frac{R}{M_{\text n}}$$ $$R_{\text s} ~=~ \frac{R}{M_{\text n}}$$ $$M_{\text n} ~=~ \frac{R}{R_{\text s}}$$ $$R ~=~ M_{\text n} \, R_{\text s}$$
Specific gas constant
$$ R_{\text s} $$ Unit $$ \frac{\mathrm{J}}{\mathrm{kg} \, \mathrm{K}} = \frac{\mathrm{m}^2}{\mathrm{s}^2 \, \mathrm{K}} $$ The specific gas constant indicates the ratio of the molar gas constant to the molar mass of a gas.
| Gas | Specific gas constant \(R_{\text s}\) |
|---|---|
| Helium (He) | \( 2077.1 \, \frac{\mathrm J}{ \mathrm{kg}\, \mathrm{K} } \) |
| Methane (CH4) | \( 518.4 \, \frac{\mathrm J}{ \mathrm{kg}\, \mathrm{K} } \) |
| Nitrogen (N2) | \( 296.8 \, \frac{\mathrm J}{ \mathrm{kg}\, \mathrm{K} } \) |
| Oxygen (O2) | \( 259.8 \, \frac{\mathrm J}{ \mathrm{kg}\, \mathrm{K} } \) |
| Carbon dioxide (CO2) | \( 188.9 \, \frac{\mathrm J}{ \mathrm{kg}\, \mathrm{K} } \) |
Molar mass
$$ M_{\text n} $$ Unit $$ \frac{\mathrm{kg}}{\mathrm{mol}} $$ Molar mass [kg / mol] of a substance is the total mass \(m\) of the gas per amount of substance \(n\): \( M_{\text n} = m/n\).
| Gas | Molar mass \(M_{\text n}\) |
|---|---|
| Helium (He) | \( 4.003 \cdot 10^{-3} \, \frac{\mathrm{kg}}{ \mathrm{mol}} \) |
| Methane (CH4) | \( 16.04 \cdot 10^{-3} \, \frac{\mathrm{kg}}{ \mathrm{mol}} \) |
| Nitrogen (N2) | \( 28.01 \cdot 10^{-3} \, \frac{\mathrm{kg}}{ \mathrm{mol}} \) |
| Oxygen (O2) | \( 32.00 \cdot 10^{-3} \, \frac{\mathrm{kg}}{ \mathrm{mol}} \) |
| Carbon dioxide (CO2) | \( 44.01 \cdot 10^{-3} \, \frac{\mathrm{kg}}{ \mathrm{mol}} \) |
Gas constant
$$ R $$ Unit $$ \frac{\mathrm J}{\mathrm{mol} \, \mathrm{K}} $$ Molar gas constant (also called universal gas constant) is a physical constant from thermodynamics and has the following exact value:$$ R ~=~ 8.314 \, 462 \, 618 \, 153 \, 24 \, \frac{\mathrm J}{\mathrm{mol} \, \mathrm{K}} $$