Thermodynamic properties of some binary mixtures containing hexafluorobenzene.

A detailed investigation into the thermodynamic properties of binary mixtures containing hexafluorobenzene is described. The excess enthalpies of mixing of hexafluorobenzene with eight amines and two hydrocarbons are presented and the excess heat capacity determined in the case of the amines. Measurements were made using a twin version of the "Larkin-McGlashan" Calorimeter. The extension to a twin calorimeter together with the advantages which ensue are fully discussed. An apparatus is described for the precise measurement of vapour pressure. The results obtained in the case of pure hexafluorobenzene are compared with other precise measurements and satisfactory agreement is found. Computer programs have been developed to calculate the excess Gibbs Function of Mixing GE from experimental vapour pressure measurements. The computer programs were tested using reliable literature data and the results were judged to be satisfactory. An apparatus to measure the volume change on mixing is described and the technique was checked by studying the benzene- cyclohexane system. The excess volume of mixing is reported for hexafluorobenzene + N,N-dimethylaniline. Preliminary investigations are reported into the use of N.M.R. and solid liquid phase diagrams in interpretting the behaviour of specifically interacting media. The results of all the thermodynamic data are discussed in terms of complex formation and the possibility of considerable stabilisation by charge transfer forces is considered. The work on aqueous solutions described in Appendix I centres around the properties of acetonitrile water mixtures. The excess volume of mixing for this system is presented at two temperatures as also are the partial molar volumes. The results are discussed in terms of solute - solvent and solvent - solvent interactions. Also presented is an analysis of the maximum density properties of aqueous solutions. Particular emphasis is placed upon alcohol water mixtures and visual correlations are explained thermodynamically. In this department some studies of the behaviour of cadmium chloride in formamide were carried out by Dr. B.L. Muju. The work done by the present author in interpretting these data is summarised in Appendix II.