Introductory Chemical Engineering Thermodynamics

Chapter 12. Van Der Waals Activity Models

Nothing is more practical than a good theory.¹

Clausius

Empirical models like the Redlich-Kister expansion provide a significant improvement over the ideal solution approximation, but they lack the kind of connection with the molecular perspective that we have developed in Chapters 1 and 7. The empirical models of Chapter 11 are useful for determining the activity coefficients from a given expression for G^E, but they suggest little about the form that G^E should assume. As we develop models that incorporate physical insight more closely, we also obtain greater predictive power.

Section 12.1 introduces concepts common to many models based on the van der Waals approach including random mixing rules and the ...