After determining the rate law for a reaction, mechanisms are proposed that fit the rate law. The chemistry of the compounds is paramount in proposing these mechanisms, but then the possibilities are narrowed by comparing with rate laws.

Many rate laws, particularly in aqueous solutions, involve an acid or base dependency even when H⁺ is not part of the overall balanced equations. An ion formed by reaction with H⁺ frequently reacts at a different rate than neutral compound. When the acid ion reacts with another compound or ion, the reaction is still a bimolecular reaction. Termolecular reactions are very slow, and many rate equations that include two compounds and H⁺ are reactions of and acid ion with a second compound not a termolecular reaction.

Reaction Mechanisms

Mechanisms and Rate Laws

Mechanisms and Rate Laws Advanced