In equation (40), W is reversible work which represents the internal free energy. Yalkowsky et al. (1976) used the molar surface area (A) and the surface tension (a) to replace the molar volume (V) and reversible work. Under those circumstances, equation (40) becomes:
where aA and aB are the surface energies of the pure liquids A and B, while aAB is the interfacial energy between the two liquids. The interfacial tension can be experimentally measured for substances of different polarity, and therefore equation (41) better predicts solubility in polar solvents.
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