What Is the Gas Constant?

The gas constant (also known as the general or ideal gas constant, usually represented by the symbol R) is a physical constant that links various thermodynamic functions in the equation of state of matter. (The ratio of the gas constant to Avogadro's constant is Boltzmann's constant.) This is a constant that characterizes the properties of an ideal gas.

A gas constant is a constant that characterizes the thermodynamic properties of an ideal gas. Is the ratio of the product of the absolute pressure p and the specific volume v of the ideal gas to the thermodynamic temperature T. It is often expressed by the symbol "R", and the unit is "J / (kg · K)". The gas constant is numerically equivalent to the expansion work performed by an ideal gas with a mass of 1 kg when the temperature is increased by 1 K in a reversible constant pressure heating process. Its value depends only on the type of gas and has nothing to do with the thermal state of the gas. For example, the R of oxygen is always equal to 259.8J / (kg · K), the R of nitrogen is always 296.7J / (kg · K), and so on. In engineering thermodynamics and other disciplines, the gas constants of various ideal gases are often calculated according to the general gas constant divided by the kilomolar mass or according to the Meyer formula. ^[2]

The value of R	unit
8.314472	J / (K · mol)
0.0820574587	L · atm / (K · mol)
8.20574587 × 10 -5	m 3atm / (K · mol)
8.314472	m 3 · Pa / (K · mol)
8.314472	L · kPa / (K · mol)
8.314472 x 10 6	cm 3Pa / (K · mol)
62.3637	L · mmHg / (K · mol)
62.3637	L · Torr / (K · mol)
1.98718	cal / (K · mol)
83.14472	L · mbar / (K · mol)

Supplementary R unit derivation:

by

The American Standard Atmospheric Administration defined the gas constant R * as:

R * = 8.31432 × 10 ³ N m kmol ^-1 K ^-1 .

Note that the use of kilomolar units results in a factor of 1000 in the constant. USSA1976 acknowledges that this value is inconsistent with the quoted values of Avogadro constant and Boltzmann constant. This difference is not a significant departure from accuracy, USSA1976 used this R * value for all calculations in a standard atmosphere. When the ISO value of R is used, the calculated pressure is increased by 0.62 Pascals over 11 kilometers (equivalent to only 17.4 cm or 6.8 inches difference) and 0.292 Pa (equivalent to 0.338 meters or 13.2 differences) at 20 kilometers inch). ^[4]