Mixing enthalpies of molecular liquids: model of contribution balance of imaginary endo- and exotherms

Abstract

To analyse enthalpy isotherms of mixing and other physicochemical properties of binary mixtures, there has been introduced a model of contribution balance of imaginary endo- and exotherms that can be used in solving a number of practical interpolation problems connected with predicting properties of binary mixtures of the composition (constant component 1–variable component 2 (homologous series)) in the absence of data for any member of homologous series, when prognosticating the temperature changes in isotherms of physicochemical properties of binary mixtures, as well as when predicting the temperatures of their stratification. As invariants of the model, there has been proposed a sum of extremums of imaginary endo- and exotherms, which is in linear connection with the integral of mixing enthalpy over the whole region of molar fractions, as well as the arithmetic mean of positions of endo- and exotherm extremums on the axis of molar fractions. For mixing enthalpies of binary systems (water–variable primary n-alcohol), linear correlations of extremum sums of endo- and exotherms with the molar volume of alcohol have been determined. Linear correlations of invariants with temperature have been ascertained. Deviations from this linear dependence point out on the occurrence of microheterogeneity in binary mixture and on its approach to stratification.

Keywords:

• empirical model
• enthalpy
• water
• alcohol
• temperature dependence