Thermodynamics of aggregation of tri-n-octylammonium halides in benzene solutions

Abstract

The freezing temperatures of dilute benzene solutions of tri-n-octylammonium halides were measured over the concentration range 0.01–0.3 mol kg^–1. The relative apparent molar enthalpies of these systems up to 0.55 mol kg^–1 were determined calorimetrically at 298.15 K. The practical osmotic coefficients and molal activity coefficients were calculated at the freezing point of benzene, i.e. 278.68 K, while the excess thermodynamic functions were calculated at 298.15 K. The non-ideal behaviour of the systems investigated was described on the basis of an association model, in which the first stepwise association reactions occur less readily than the rest. Thereby, the association equilibria were treated by two independent parameters: the dimerization constant β₂ and constant K, both of which were obtained from the experimental data by a curve-fitting method.