Dissolution enthalpy of NaCl in aqueous nonelectrolyte solutions at 298.15 K. Analysis of electrolyte–nonelectrolyte enthalpic pair interaction coefficients in aqueous solution

Enthalpies of solution of NaCl in aqueous solutions of isopropanol, s-butanol, 2-methoxyethanol, 2-ethoxyethanol, acetone, and N,N-dimethylformamide were measured. The results of enthalpy measurements were analyzed from the point of view of the effect of added nonelectrolyte on water structure, and enthalpic pair interaction coefficients hxy{(Na+ + Cl−)–nonelectrolyte} were calculated and compared with appropriate data for (Na+ + I−)–nonelectrolyte pairs. The group additivity concept appeared to be useful for the analysis of calculated hxy coefficients. The correlations between hxy and the functions characterizing different properties of the solutes under study were examined. It was shown that the correlation with the heat capacity of transfer of the nonelectrolyte molecule from the vapour phase to high dilution in water was the most promising. The interpretation of observed correlations was proposed.

Enthalpies of solution of urea in water–alkanol mixtures and the enthalpic pair interaction coefficients of urea and several nonelectrolytes in water

Enthalpies of solution of urea in binary mixtures of isopropanol, s-butanol, and ethoxyethanol with water have been measured at high water content. Those in the binaries isopropanol + water and ethoxyethanol + water show endothermic maxima at 8 and 4 mol% alkanol, respectively. Enthalpic pair interaction coefficients are calculated for the interactions between urea and the alkanols and discussed in connection with these coefficients for interactions between urea and other nonelectrolytes and between N,N-dimethylformamide and several nonelectrolytes. The enthalpic pair interaction coefficients correlate linearly with the heat capacity change on hydration of the nonelectrolytes and with the enthalpy of hydrophobic hydration of the alkanols.