"The theoretical basis of this book is developed ab ovo. This requires dealing with several problems arising in physical chemistry including the concept of entropy as a thermodynamic coordinate and its relation to probability. Thus Maxwell Boltzmann and Gibbs statistical thermodynamics, and quantum statistics are made considerable use of. A statistical mechanical derivation of the law of mass action for gases and solids is presented, and the problems arising in the application of the law of mass action to the liquid state are addressed. Molecular interactions and how to take them into account when deriving the law of mass action is discussed in some detail sketching a way alternativ to the use of activities. Finally, attention is drawn to the statistical mechanical background to Linear Free Energy Relationships (LFER's) and of Isokinetic Relationships (IKR's) and their connections with molecular interactions. "--BOOK JACKET.