Excess thermodynamic quantitites in binary systems of non-electrolytes 3. Graphical representation—application to water-acetonitrile systems

Abstract

Douhéret, G., Moreau, C. and Viallard, A., 1986. Excess thermodynamic quantities in binary systems of non-electrolytes. 3. Graphical representation—application to water-acetonitrile systems. Fluid Phase Equilibria, 26: 221–249. We have shown in previous work that excess quantities of a large number of thermodynamic variables could be calculated using a very general method which provides rigorous expressions for the corresponding ideal mixing laws. These are often non-linear expressions of concentrations. They sometimes take the form of a ratio of ideal quantities, in which case the weighting coefficients specific to each component cannot always be made explicit. The consequences of the analytical form of these laws with regard to the graphical representation of the excess quantities warrant examination. Here, we have looked at the implications for binary systems. Several approaches are described. The first involves a representation which allows for the fact that the sum of the weighting coefficients is variable and equal to J (nl), which is a function of the composition of the system. The second involves making this sum a constant, J (l) and J (l), usually equal to 1, either by arranging for the concentration scale to be linear, or by double linearization of the ideal mixing laws, or by using a reference concentration scale. The advantages and drawbacks of these approaches are discussed.