Key equations for Process Engineers Thermodynamics

Universal Gas Constant

The behaviour of an Ideal gas is described by the following equation,

PV = nRT


P = Pressure (bar, atmosphere, Pa)

V = Gaseous volume (m3, cm3)

n = number of gaseous moles (dimensionless)

R = Universal gas constant (J/mol.K, lit.atm/mol.K)

T = Temperature of the gas (K, 0C)

The universal gas constant is also known by alternative names such as Ideal gas constant, molar gas constant or simply, gas constant.

The universal gas constant is common for all the gases and the numerical value of this constant depends on the units used to describe the remaining entities in the Ideal gas equation, such as pressure, temperature, and volume.

For different combinations of units, numerical values of Universal gas constant are given by following list,

Units ( P.V / n.T )                                          Value of R

J/K.mol                                                           8.314

cal/K.mol                                                        1.986

erg/K.mol                                                       8.314X107

lit.kPa/K.mol                                                  8.314

m3.Pa/K.mol                                                  8.314

cm3.MPa/K.mol                                             8.314                                                 8.314X10-5

cm3.atm/K.mol                                               82.06                                                   8.314X10-2

lit.atm/K.mol                                                  0.082

lit.mmHg/K.mol                                             62.364

lit.torr/K.mol                                                   62.364

ft.lbf/K.gmol                                                   6.132

ft.lbf/                                               1545.35

ft3.psi/                                             10.732

ft3.atm/                                           0.730

ft3.mmHg/                                        998.97


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