through any subsequent transition state depends on the Gibbs energy of that state relative to the lower-energy intermediate. The rate-determining step is then the step with the largest Gibbs energy difference relative either to the starting material or to any previous intermediate on the diagram. Also, for reaction steps that are not first-order, concentration terms must be considered in choosing the rate-determining step. Chain reactions Not all reactions have a single rate-determining step. In particular, the rate of a chain reaction is usually not controlled by any single step. Diffusion control In the previous examples the rate determining step was one of the sequential chemical reactions leading to a product. The rate-determining step can also be the transport of reactants to where they can interact and form the product. This case is referred to as diffusion control and, in general, occurs when the formation of product from the activated complex is very rapid and thus the provision of the supply of reactants is rate-determining. See also Product-determining step Rate-limiting step (biochemistry) References Chemical kinetics ja:反応速度#律速段階