Rate-Determining Step

• The rate-determining step (RDS) is the slowest step in a chemical reaction and therefore, determines the overall reaction rate.
• It possesses the highest energy threshold or activation energy (Ea) in the reaction pathway.
• The molecularity of the rate-determining step dictates the order of the reaction. For instance, if two molecules react in the RDS, the reaction is second order.
• The number and type of reactant species involved in the RDS directly influences the rate law. This means that changing the concentration of the reactants involved in this step will change the overall reaction rate.
• In multi-step reactions, the intermediates are usually part of the rate-determining step. These intermediates are formed in the steps before the RDS and consumed in the RDS.
• Any catalyst that reduces the activation energy of the rate-determining step will increase the speed of the overall reaction.
• Reaction mechanisms are proposed based on the rate equation, and these mechanisms always include a slow, rate-determining step.
• In terms of potential energy diagrams, the RDS corresponds to the highest peak on the graph, signifying the greatest energy barrier the reaction must overcome to progress.
• The steady-state approximation is sometimes used to simplify rate equations. It assumes that concentrations of intermediates, formed and consumed in the RDS, remain constant over time.
• The Rate-Determining Step principle is key to the study of chemical kinetics in various contexts, such as atmospheric chemistry, biological reactions, combustion reactions, and industrial processes.