Semiempirical binary interaction parameters

These models are semiempirical and are based on the concept that intermolecular forces will cause nonrandom arrangement of molecules in the mixture. The models account for the arrangement of molecules of different sizes and the preferred orientation of molecules. In each case, the models are fitted to experimental binary vapor-liquid equilibrium data. This gives binary interaction parameters that can be used to predict multicomponent vapor-liquid equilibrium. In the case of the UNIQUAC equation, if experimentally determined vapor-liquid equilibrium data are not available, the Universal Quasi-chemical Functional Group Activity Coefficients (UNIFAC) method can be used to estimate UNIQUAC parameters from the molecular structures of the components in the mixture3. 

For ternary and stiU more complex systems, the general approaches are the same. But for these systems, not only must the relations for the liquid phase be modified, but also those for the solid phase. A comprehensive review on phase equilibria in ternary III-V systems has been written by Panish and Ilegems [21]. A useful semiempirical expression for the calculation of the solid-solution interaction parameter, based on the difference in the lattice constants of the binary constituent compounds, has been developed by Stringfellow [22]. 

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