Partial molar heat capacities and structural effects of tetra-n-pentylammonium bromide in aqueous urea and aqueous sodium chloride solutions

Abstract

The partial molar enthalpies of tetra-n-pentylammonium bromide in aqueous urea (up to 7 M urea) and in aqueous sodium chloride (up to 5 M NaCl) solutions have been determined calorimetrically at 25 and 35°C. These data have been used to derive the enthalpies of transfer (at 25 and 35°C) and the heat capacities of transfer (at 30°C) of the salt from water to aqueous urea and aqueous sodium chloride solutions. The results show that the heat capacities of transfer in aqueous urea and aqueous sodium chloride solutions have opposite signs. It has been deduced that the structure breaking effect of urea in the presence of hydrophobic solutes or ions containing hydrophobic parts is different from that of sodium chloride.