Gibbs energy residual-property relation

The residual Gibbs energy and the fugacity coefficient are useful where experimental PVT data can be adequately correlated by equations of state. Indeed, if convenient treatment or all fluids by means of equations of state were possible, the thermodynamic-property relations already presented would suffice. However, liquid solutions are often more easily dealt with through properties that measure their deviations from ideal solution behavior, not from ideal gas behavior. Thus, the mathematical formahsm of excess properties is analogous to that of the residual properties. 

We note with respect to this equation that all terms have the units of m moreover, in contrast to Eq. (10.2), the enthalpy rather than the entropy app on the right-hand side. Equation (13.12) is a general relation expressing as a function of all of its canonical variables, T, P, and the mole numb reduces to Eq. (6.29) for the special case of 1 mole of a constant-compo phase. Equations (6.30) and (6.31) follow from either equation, and equ for the other thermodynamic properties then come from appropriate def equations. Knowledge of G/RT as a function of its canonical variables evaluation of all other thermodynamic properties, and therefore implicitly tains complete property information. However, we cannot directly exploit characteristic, and in practice we deal with related properties, the residual excess Gibbs energies. 

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