The Two-Parameter UNIQUAC Model

The Universal Quasichemical (UNIQUAC) is a two-parameter (t12, x21) model based on statistical mechanical theory. Activity coefficients are obtained by 

Segment or volume fractions, q , and area fractions, 0 and 0, are given by 

Parameters r, q and q are pure component molecular-structure constants depending on molecular size and external surface areas. For fluids other than water or lower alcohols, q = q.  

For each binary mixture there are two adjustable parameters. t 2 and t2). These in turn, are given in terms of characteristic energies All 12 —1LI 12—1 22 and Au21=u2,-un given by 

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