Thermochemical and volumetric properties of aqueous urea systems. Heat capacities and volumes of transfer from water to urea—water mixtures for some 1 : 1 electrolytes at 298.15 K

Abstract

This paper reports densities, apparent molar volumes and apparent molar heat capacities at 298.15 K for sodium chloride, tetraphenylarsonium chloride and sodium tetraphenylboron in water and aqueous urea solutions containing 5, 10, 20 and 30% urea by weight. Standard-state properties have been calculated from these data which in turn have been used to calculate volumes and heat capacities of transfer for the bulk electrolytes. Single-ion thermodynamic properties have been calculated using the tetraphenylarsonium—tetraphenylboron reference electrolyte assumption. Interpretation of the trends observed in these data are discussed in terms of structural interactions within the system. In addition, densities, apparent molar volumes and apparent molar heat capacities are reported for solutions of urea in water at concentrations up to 16 mol kg^–1 at 288.15, 298.15, 308.15 and 313.15 K.