Dependence of G^{E }on temperature and pressure
The idea of the molar excess property has been introduced in section 6.5 with the following definition:
M^{E} = M – M^{id}(6.163)
Typically the property M can be an intensive property such as: V, U, H, S, G, A, etc. The relations between the molar excess properties of V, H and G is particular significant for description of nonideal solution thermodynamics. One may start from the generic total derivative of the Gibbs free energy for a real solution and an ideal solution in the same way as eqns. 5.27 and 5.28:
One may write the same equation specifically for an ideal solution, whence:
 
Thus subtracting eqn. 6.165 from 6.164:  
Thus we may write the following further generative relations:
 
And further:
