Thermodynamics of bolaform electrolytes. V. Enthalpies and heat capacities in aqueous urea solutions

The partial molal heats of solution at infinite dilution of 1,4-bis(triethylammonium)butane dibromide and 1,10-bis(triethylammonium)decane dibromide in aqueous urea (up to 8m urea) have been determined calorimetrically in the temperature range 18–33°C. These data have been used to derive the partial molal heat capacities at infinite dilution, the enthalpies of transfer, and heat capacities of transfer at infinite dilution from water to urea-water solutions. The results show that the enthalpies of transfer are negative and decrease with increasing urea concentrations. The heat capacities of transfer are negative at low urea concentrations and increase in magnitude at higher urea concentrations. In the case of the smaller cation the partial molal heat capacity in 8m aqueous urea solution is greater than in pure water. The results are discussed in terms of structural changes in the solvents on dissolution.