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Molar gas constant

Molar gas constant (also known as universal gas constant, usually denoted by symbol R) is the constant occurring in the universal gas equation, i.e. the equation of state of an ideal gas:

pV = nRT
Here p is the pressure of gas, V the volume it ocupies, n the number of moles of gas, and T its temperature.

It can be shown that R is an universal constant, equal for all gases. Real gases obey this equation only in an approximation of very diluted gases.

R also appears in other popular equation, e.g. Nernst's.

Its value is:

R = 8.314570(70) J K-1 mol-1

The two digits in parentheses signify the uncertainty (standard deviation) in the last two digits of the value.

The Boltzmann constant kB is defined as a ratio of molar gas constant and the Avogadro's number: