“Structure promotion” and “structure breaking”. Heat capacities of caesium bromide, tetramethylammonium bromide and tetra-n-butylammonium bromide in several solvents from 278 to 328 K

Abstract

Enthalpies of solution of caesium bromide and tetramethylammonium bromide have been measured calorimetrically in water, formamide, N-methylformamide and N-methylacetamide from 278 to 328 K at 10 K intervals. Application of the integral enthalpy method yields partial molar heat capacities at infinite dilution which have been split up into two contributions: one is due to the intrinsic heat capacity of the ions while the second arises from the influence of the ions on solvent structure. The value of the latter contribution appears to be zero for tetra-n-butylammonium bromide in NN-dimethylformamide. On this basis it is possible to demonstrate ion-solvent interactions for this salt in other solvents more directly. The results for all of the salts are discussed in terms of different structural changes in the solvents on dissolution.