A chain reaction involves intermediates generated in one step leading to intermediates in subsequent steps. Radicals and ions can act as chain carriers that propagate the reaction. Initiation steps form the initial chain carriers. Propagation steps produce new carriers from reactants. Branching steps generate multiple carriers from a product. Termination and inhibition steps end the chain reaction. The rate law for the pyrolysis of ethanal follows the Rice-Herzfeld mechanism and is third order with respect to ethanal concentration.