23   The Components of the Rest Energy of an Amount of Gas

 
The total energy  E  of an ideal gas, enclosed in the volume  V  at the pressure  P , is the sum of three terms:

E jM · c2  +  j+ jP · V j M · c2  +  H

The meaning of those terms is the following:

The enthalpy  H  =  U  +  P · V   is the sum of thermal and mechanical energy contained in the 'hot' gas. H  is ( as  U  and  P · V ) an extensive state variable
( cf. sections 1 and 35 ).