Solution thermochemistry of NH4Br, Et4NBr, and Bu4NBr in water at 25 and 40°C

The calorimetric enthalpies of solution and enthalpies of dilution of aqueous solutions in water at 25 and 40°C were determined for NH 4 Br, Et 4 NBr, and Bu4NBr in the concentration range m = 0.006-8.3 mol electrolyte/kg solvent. The relative partial molal enthalpies of water (L 1 ) and the electrolytes (L 2 ) in aqueous solutions and the enthalpy coefficients of electrolyte-electrolyte pair interactions in water were calculated. L 1 and L 2 behave differently with temperature change in aqueous solutions of hydrophilic and hydrophobic compounds. The enthalpy, coefficient of electrolyte-electrolyte pair interactions in water for an electrolyte with a hydrophilic cation (NH 4 Br) is negative and is in fact temperature-independent. For a well-defined hydrophobic electrolyte (Bu4NBr), this coefficient is positive and is a strong function of temperature.