Perfect-Gas Properties

The molar Helmholtz energy A = Af /n of a pure perfect gas may be obtained by integration of eq 3.15 subject to the equation of state, p = —(5 P /5Fm) = nKT/ V, and an expression for the perfect-gas molar heat capacity at constant volume, C y T) = T dS /dT)y. Starting from a reference state defined by temperature T and amount-of-substance density pjf , the result is  

A parallel route to the same properties starts with the molar Gibbs energy of a pure perfect gas. This is obtained by integration of eq 3.16 starting from a reference state defined by temperature and pressure at which GP8 = + / - TS. The result is  

In order to make the two approaches consistent, one must choose the same reference state, and this requires that p =RT p  

The principal perfect-gas thermodynamic properties of pure substances and multi-component mixtures determined from these relations are summarised in Table 3.2.  

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