Molar gas constant

In chemistry, chemical engineering and physics, the molar gas constant R is a fundamental physical constant which appears in a large number of fundamental equations in the physical sciences, such as the ideal gas law and the Nernst equation. It is equivalent to the the Boltzmann constant (k_B) times Avogadro's constant (N): R = k_BN_A.

It has a defining value of:

R = 8.314472(15) J · K^-1 · mol^-1

The gas constant occurs in the ideal gas law as follows:

$P={\frac {nRT}{V}}={\frac {RT}{V_{\rm {m}}}}$

where:

P is the gas absolute pressure

T is gas absolute) temperature

V is the volume the gas occupies

n is the number of moles of gas

V_m is the molar volume

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 specific gas constant, which can be denoted as $R_{s}$. The specific gas 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 specific gas constant without denoting it as such or stating that it is the specific gas constant. This can and does lead to confusion for many readers.