A gas constant is a constant value that is denoted by R and is expressed in the terms of a unit of energy per temperature increment per mole. It is used as a constant in the famous ideal gas equation and Nernst equation. In this article, we look at the units and values of the universal gas constant.
Universal gas constant
The gas constant symbolized as “R” is also known as “universal gas constant” or “ideal gas constant”.
- The Gas constant is the physical constant in the equation for the Ideal Gas Law: PV=nRT (Where P is pressure, V is the volume and n is the number of moles and T is temperature)
- It is also seen in the Nernst equation which is relating to the reduction potential of a half-cell to the standard electrode potential: E = E0 – (RT/nF)lnQ.
- The relationship of universal gas constant with Boltzmann’s constant can be expressed as R = kB NA
Gas constant in different units
Unit for gas constant varies depending upon other units used in the equation. The most commonly used value is 8.3145 J/mol·K. Some values in different units are listed below
| Gas Constant Value | Units |
| 8.3144598(48) | J⋅K−1⋅mol−1 |
| 8.3144598(48)×103 | amu.m2.s-2.K-1 |
| 8.3144598(48)×10−2 | L.bar.K-1.mol-1 |
| 8.3144598(48) | m3.Pa.K-1.mol-1 |
| 62.363577(36) | L.Torr.K-1.mol-1 |
| 1.9872036(11)×10−3 | kcal.K-1.mol-1 |
| 8.2057338(47)×10−5 | m3.atm.K-1.mol-1 |
| 0.082057338(47) | L.atm.K-1.mo |
Specific gas constant
Specific gas constant is also known as an individual has constant and is indicated as R or Rgas. It can be obtained by dividing the universal gas constant by the molar mass (M) of pure gas.
You can check the individual gas constants for various gases here.
How to calculate the specific gas constant for gases?
The specific gas constant is not the same for all gases. For example, let us calculate the specific gas constant for carbon dioxide. The molecular weight of carbon in 44 g/mol.
So the individual gas constant for carbon dioxide gas will be = 8.31/44 = 0.188 [KJ/Kg K].
