Thermodynamic studies of some anion-exchange equilibria. Part 3.—Determination of standard enthalpy changes of uni-bivalent exchange processes

Abstract

Anion-exchange isotherms for the sulphate-chloride exchange system in the temperature range 25–65°C have been established for resins of various degrees of cross-linking and the free energy changes evaluated by two methods.^1,2 The difference between the corresponding values so obtained is small and the differences between the corresponding values of the enthalpy changes derived using the van't Hoff isochore are less than the variation due to experimental error. Preliminary studies of the selenate-chloride and oxalate-chloride systems lead to the same conclusion. Accordingly the use of the simpler relationship to derive ΔG° and ΔH° is advocated. Calorimetric measurements have been made of the enthalpy changes for reactions of the type, text-decoration:overline2Cl ^–+B^2– text-decoration:overlineB ^2–+2Cl^–, using an isothermal solution calorimeter. The values obtained are compared with those from the isotherm data and are combined with the values of ΔG° previously reported to obtain the entropy changes.