Transition State Theory

Transition state theory is a framework in physical chemistry for explaining and predicting the rates of chemical reactions, developed independently by Henry Eyring in the United States and by Meredith Gwynne Evans and Michael Polanyi in Britain, all publishing their versions in 1935. The theory holds that reactant molecules must pass through a high-energy, unstable configuration called the transition state, or activated complex, on the way from reactants to products, and treats this transition state as being in a quasi-equilibrium with the surrounding reactants. Applying statistical mechanics to that quasi-equilibrium yields the Eyring equation, which relates a reaction's rate constant to the temperature and to the free energy of activation required to reach the transition state. Transition state theory became a central tool of physical chemistry for understanding how reaction rates depend on temperature, molecular structure and catalysis.