Introductory Chemical Engineering Thermodynamics

Chapter 13. Local Composition Activity Models

I have constructed three thousand different theories in connection with the electric light... Yet, in only two cases did my experiments prove the truth of my theory.

Thomas A. Edison

It is evident from Chapter 12 that describing solution nonideality with van der Waals’ mixing rules is imprecise. With a single parameter like k₁₂ or A₁₂, we can match the magnitude of the excess energy, but not the skewness. The Margules two-parameter and van Laar models address this problem in an ad hoc fashion, but there is no physical basis for extending these to multiple components. A rational basis for extending the analysis of mixtures should seek a legitimate explanation for the source of varied skewness. One ...