A previously described method of calculation, using bond dissociation and solvation energies and electron affinities as the main terms, is elaborated and extended to calculate free energies of activation and reaction of a wide variety of aromatic S_N reactions, and corresponding acid–base reactions. These have been tested in many cases against experimental data, with reasonable, often very good, agreement. Data are discussed in terms of kinetic and thermodynamic nucleophilicity and basicity. The procedure is considered generally applicable to exchange reactions in organic and inorganic systems.