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In a reaction mechanism, (a) what is the difference between an activated complex
and an intermediate? (b) What is meant by the rate-determining step? Which
elementary reaction in a reaction mechanism is often the rate-determining step?
(a) An activated complex is the structure along the reaction pathway of the highest energy, which determines the activation energy for the reaction. An intermediate can be any structure found in the reaction path.
(b) The rate-determining step is the elementary reaction that controls the mathematical form of the overall rate law. The rate-determining step is usually the slowest elementary reaction.