Solution Thermochemistry of NH_4Br, Et_4NBr, and Bu_4NBr in Water at 25 and 40 deg C

摘要

The calorimetric enthalpies of solution and enthalpies of dilution of aqueous solutions in water at 25 and 40 deg C were determined for NH_4Br, Et_4NBr, and Bu_4NBr in the concentration range m = 0.006-8.3 mol electrolyte/kg solvent. The relative partial molal enthalpies of water (L-bar _1) and the electrolytes (L-bar _2) in aqueous solutions and the enthalpy coefficients of electrolyte-electrolyte pair interactions in water were calculated. L-bar _1 and L-bar _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_4Br) is negative and is in fact temperature-independent. For a well-defined hydrophobic electrolyte (Bu_4NBr), this coefficient is positive and is a strong function of temperature.