A general “geometric” thermodynamic model for multicomponent solutions

Several “geometric” models have been proposed for estimating thermodynamic properties of a ternary solution from optimized data for its binary subsystems. The most common are the Kohler, Muggianu, Kohler/Toop, and Muggianu/Toop models. The latter two are “asymmetric” in that one component is singled out, whereas the first two are “symmetric”. The use of a symmetric model when an asymetric model is more appropriate can often give rise to errors. There are 64 possible simple geometric models for a ternary system. Equations are developed to calculate the thermodynamic properties of an N-component solution (N>3) in a rational manner while permitting complete flexibility to choose any of the 64 possible geometric models for any ternary subsystem. An improved general functional form for “ternary terms” in the excess Gibbs energy expression is also proposed.