Modern aspects of thermodynamics and structure of nonaqueous solutions*

A set of general questions about the thermodynamics of ionic processes in non—aqueous solutions and their dependence on composition and external conditions is discussed; thermodynamic approaches for ascertaining the role of a solvent, thermodynamic characteristics of solvation, methods of definition of standard thermodynamic characteristics, properties of non— aqueous solutions at lowered temperatures, and influence of microadmixtures. Thermodynamic methods of investigating solutions are considered. The fruitfulness and universitalityof ascertaining the solvent role in chemical reactions, their effectiveness for studying structural changes of solvents and solutions with change of external factors (temperature, pressure) nature of additions, composition and others is presented. The advantage over many other solution investigation methods is that they characterize structural changes of solutions, taking into account both energetic and entropy factors. Studies take into account the double function of a solvent, i.e. as medium and as chemical reagent. The absence of thermodynamic data for individual ions in solution is marked. To ignore the different types of ion—molecular interactions for cations and anions, and the thermodynamics of coordination and solvation of individual ions is a major disadvantage. Different methods of obtaining the standard thermodynamic characteristics based both on extrapolation and non—extrapolation approaches are discussed. The problems of creation of a physico—chemical 'passport system' of non— aqueous solutions, data banks and others is considered. The properties of non—aqueous solutions at lowered temperatures, the influence of added water and the constituent gases in air are of specific interest. Attention is paid to the need of the correct analysis of composition— property diagrams and their rationalization, pointing to choices of composition and property indices at which a linear dependence between them in an ideal system is observed. The influence of the solvent on solubility, physico—chemical properties and state of species in solutions are considered with other issues. Numerous examples illustrating the investigation are given. INTRODUCTION The scientific and practical importance of the chemistry of non—aqueous solutions is clear from the existence of many chemical reactions, including industrial processes, which cannot proceed in the presence of water. By participating directly in a chemical process the solvent is a determining factor of that process. Thus new methods of inorganic and organic synthesis, using multicomponent mixtures and diversification of technological procedures can develop. The solvent has a double role both as the medium and as a reagent. While chemical properties of the solvent influence the reactant's solvation processes remain of primary importance. * Section lecture presented at 10th International Conference on Nonaqueous Solutions (Leuven, Belgium : 17—21 August 1986). Manuscript was not available when other lectures from the Conference were published (Pure Appl. Chem. Vol. 58, No. 8 (August 1986), pp. 1077—1170)