Topic overview

Start with the big picture

An elementary step represents a single molecular event, and its molecularity determines its rate law. The overall rate law, however, cannot be inferred from the balanced reaction alone; it must agree with experimental kinetics and a plausible sequence of steps. Because intermediates do not appear in the net equation, pre-equilibrium and steady-state approximations can be used to express rates without them. The topic also considers special cases, including catalytic and chain reactions and enzyme kinetics. Arrhenius analysis, the Hammond postulate, and kinetic isotope effects provide ways to relate reaction rates to temperature and molecular events. Together, these ideas offer criteria for assessing mechanistic proposals and avoiding common interpretation errors.