Thermodynamic Properties of Regular Solutions

In the regular solution, specific interactions such as hydrogen bonding, acid-base association, and charge transfer do not occur, but the intermolecular forces are no longer equal. That is, the energies associated with A-A and B-B interactions are not equal to the A-B interactions. Under these conditions, if the molecules are about the same size, it can be shown that G is given by 

Starting with equation (17.19), equations for the activity coefficients can be derived. For n = ( i + n-i) total moles, equation (17.19) becomes 

Differentiating equation (17.20) with respect to rt while holding 2 constant and remembering that xi and X2 are functions of tt gives, after some manipulation, the following relationship for In 71 

Equations for the other excess properties can also be obtained. Starting with 

It should not be surprising to find out that most nonelectrolyte solutions are not ideal, nor are they regular.8 Equations such as (17.19) or (17.25) do not adequately describe the functional dependence of (7, H, or on concentration. Extended forms are often used. A common one is the Redlick-Kister equation given by 

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