Elements of Transition-State Theory in Relation to the Thermal Dissociation of Selected Solid Compounds

Abstract

An analysis was carried out on the thermal dissociation of selected inorganic salts according to Transition-State Theory (TST). For this purpose, two possibilities were compared in the context of rate constants: in the first case using the Arrhenius constant directly from TST, and in the second, using the thermodynamic equilibrium constant of the reaction/process of active state formation. The determined relationships are presented in the form of temperature profiles. It was established that TST applies to reactions for which there is a formally and experimentally reversible reaction, in the literal sense or catalytic process. The importance of the isoequilibrium temperature, which results from the intersection of the thermodynamic temperature profile and the Gibbs free energy of activation, was demonstrated. Its values close to the equilibrium temperature are indicative of more dynamic kinetic qualities. As part of the discussion, the Kinetic Compensation Effect (KCE) was used to observe changes in the entropy of activation by comparing two kinetic characteristics of the same reaction. Enthalpy–Entropy Compensation (EEC) was shown to be the same law as KCE, just expressed differently. This was made possible by TST, specifically the entropy of activation at isokinetic temperature, by which the perspective of the relationship of energy effects changes.

Keywords

• solid state
• Transition-State Theory (TST)
• reversible reactions
• phenomenological thermodynamics
• activation temperature
• isoequilibrium temperature