Some thermodynamic measurements relating to solution processes

Abstract

The interest in this thesis is the thermodynamic approach to the elucidation of the structures of dilute ionic solutions. Solvation enthalpies of group Ia,IIa and VIIb ions in water, forraamide and the two N-methyl derivatives of forraamide are derived from recently published heat of solution data and from heat of solution measurements made by the author, and are compared with theoretical values calculated using an extended form of Buckingham's theory. The interpretation of solvation entropies suggests that certain structural effects occur in the process of ion solvation. By including these in the theoretical calculations, good agreement between experiment and theory is obtained. The experimental results presented include: (a) the standard enthalpies of formation and solution in water of magnesium bromide, magnesium iodide, and all of the group IIa fluorides; (b) the standard enthalpies of solution in water of the group II bromates, and of a number of tetra-alkylammonium salts; (c) the standard enthalpies of solution in formamide, N-methylformamide and N,N-dimethylforraamide of a number of group IIa halides and halates. The following thermodynamic parameters are calculated for the group Ia and IIa halides and halates using the most modern data available: standard enthalpies of formation, lattice enthalpies, solvation enthalpies, entropies in the gas solution and solid state, solvation entropies, lattice entropies, lattice free energies, solvation free energies. Some consideration is given to the estimation of solvation parameters for complex ions. Using a new empirical approach, the corresponding functions for the individual ions are derived. An account is given of the construction and method of use of the calorimeter, and of an apparatus for the isopiestic comparison of vapour pressures.