Molar gas constant

In chemistry and physics, the molar gas constant R is a physical constant with the value:   8.314 472  J mol⁻¹K⁻¹.

The constant R is equal to the Boltzmann constant times Avogadro's constant: R = k_BN_A.

The constant arises in equations of state, most notably in the ideal gas law

$R={\frac {pV_{m}}{T}},$

where p is the pressure, V_m the molar volume, and T the absolute temperature of the ideal gas.

Notation for the gas constant

The gas constant defined in this article is the universal gas constant, $R$, that applies to any gas. There is also a gas-specific version of the gas constant, which can be denoted as $R_{s}$. The gas-specific constant is defined as $R_{s}=R/M$ where $M$ is the molecular weight.

Unfortunately, many authors in the technical literature sometimes use $R$ as the gas-specific constant without denoting it as such or stating that it is the gas-specific constant. This can and does lead to confusion.