Behaviour of the Excess Functions

The applicability of corresponding-states theories of liquid mixtures has been tested for all the dense gas systems for which the excess functions have been directly determined. 186-139 results are inconclusive. For many of the mixtures studied there is a large difference in the critical temperatures between the components. In such cases, as shown above, the excess functions at moderate pressures depend primarily on the properties of the component of higher critical temperature - they are insensitive to the details of the mixed interactions. At higher pressures, where the test of theory is more significant, the calculated properties depend markedly on the choice of reference fluid. Even simple 

Malesinska and J. Stecki, Proceedings of the 3rd International Conference on Chemical Thermodynamics, Baden, 1973, Vol. II, p. 146. 

In general the two-fluid average potential model gives better results than the one-fluid model. The three-fluid model counts all binary inter actions and is, therefore, properly used at low densities. The van der Waals one-fluid 

Summary of direct measurements of excess functions of moderately dense gases. Numbers indicate references in body of text 

Prigogine, Molecular Theory of Solutions , North-Holland, Amsterdam, 1957. 

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The existence of two complexes in this case is clearly implied by the chemical structures and by the unsymmetrical behaviour of the excess functions. Kearns... 

Behaviour of the Excess Functions.—Some characteristic F data are shown in Figure 8. At low pressures both F and H lp are consistent with equation-of-... 

The theorem of correspondii states can therefore be applied to the mixture as well as to pure compounds, when the average molecular parameters of the mixture are known. A simple graphical discussion of the excess properties is then possible (cf. 4). One can read the values of the excess functions directly from a diagram representing the reduced properties of pure compounds as functioJ3s of reduced temperature and pressure. This is the most remarkable feature of the theory, if one keeps in mind the complex relationship among the excess functions themselves and between excess functions and intermolecular forces. In the present treatment the behaviour of the excess functions is directly related to the behaviom of pure components which may be either obtained experimentally or deduced from some statistical model. 

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