Topic overview

Start with the big picture

A reaction’s rate law describes how its rate responds to reactant concentrations, while its overall order is determined experimentally and need not match the reaction’s stoichiometry. For an elementary step, molecularity provides the basis for its rate law. In a multistep mechanism, the slow rate-determining step helps govern the observed kinetics; steady-state and pre-equilibrium approximations can simplify expressions involving intermediates. Collision theory and the Arrhenius equation relate reaction rates to molecular encounters and temperature, while transition state theory and reaction-coordinate diagrams describe barriers and activated complexes. The broader topic also considers isotope effects, pressure-dependent unimolecular reactions, chain and photochemical reactions, diffusion control, and additional kinetic models.