Reaction mechanisms

Abstract

This chapter describes reaction mechanisms. Many reactions occur in a series of steps called elementary reactions, each of which involves only one or two molecules or ions. The molecularity of an elementary reaction is the number of molecules coming together to react. The chapter then looks at the formulation of rate laws. In a pre-equilibrium, it is assumed that an intermediate establishes a rapid equilibrium with the reactants and the subsequent formation of products is slow. In the steady-state approximation, it is assumed that the concentrations of all reaction intermediates remain constant and small throughout the reaction. The chapter also considers the rate-determining step, which is the slowest step in a reaction mechanism that controls the rate of the overall reaction. Provided a reaction has not reached equilibrium, the products of competing reactions are controlled by kinetics. Finally, the chapter discusses the Lindemann mechanism of ‘unimolecular’ reactions.