An Empirical Approach to Non-Ideal Solutions

Most real solutions are neither ideal nor regular. As a result a realistic description of their thermodynamic properties must consider the fact that both the excess enthalpy of mixing, and excess entropy, are non- zero. Wilson 

Consider the solution composed of two molecules A and B. The number of A-A interactions, with respect to the number of A-B interactions, habj is given by the overall ratio of A to B in the solution weighted by factors which account for the enthalpy associated with these interactions, namely, A b- 

Similarly, estimating the ratio of the number of B-B interactions to A-B interactions, one obtains 

The volume fractions of each molecule, Ca and Cb, are then defined using these ratios and the molar volumes of the two pure components, Vj a nd 

Subtracting off the Gibbs energy of mixing for the ideal solution (equation (1.6.11)), one obtains for Aj ixC  

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