The UNIQUAC model was initially published by Denis S. Abrams and John M. Prausznitz in the AIChE Journal, Vol. 21, No. 1, **1975**, p 114-128 as Statistical Thermodynamics of Liquid Mixtures: A New Expression for the Excess Gibbs Energy of Partly or Completely Miscible Systems. It was latter modified by T. F. Anderson and John M. Prausznitz in Industrial and Engineering Chemistry Process Design and Development , Vol. 17, No. 4, **1978**, p 552-567 as Application of the UNIQUAC Equation to Calculation of Multicomponent Phase Equilbria. 1. Vapor-Liquid Equilibrium. In the initial paper, the terms q and q’ were combined. These terms were broken out in the second paper.

UNIQUAC equation and excess UNIQUAC Gibbs free energy

Pure component parameters: r, q, q’

Binary parameters: u_{ij}, u_{ji}

UNIQUAC activity coefficients

Binary reduced form

The variable z in the equation is the coordination number and is usually set to 10.