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Chemistry LibreTexts

15: Reaction mechanisms

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    • 15.1: Elementary Steps
    • 15.2: The Steady-State Approximation
      When a reaction mechanism has several steps of comparable rates, the rate-determining step is often not obvious. However, there is an intermediate in some of the steps. An intermediate is a species that is neither one of the reactants, nor one of the products. The steady-state approximation is a method used to derive a rate law. The method is based on the assumption that one intermediate in the reaction mechanism is consumed as quickly as it is generated. Its concentration remains the same in a
    • 15.3: The Lindemann Mechanism
      The Lindemann mechanism was one of the first attempts to understand unimolecular reactions. Lindemann mechanisms have been used to model gas phase decomposition reactions. Although the net formula for a decomposition may appear to be first-order (unimolecular) in the reactant, a Lindemann mechanism may show that the reaction is actually second-order (bimolecular).
    • 15.4: Some Reaction Mechanisms Involve Chain Reactions
      Chain reactions usually consist of many repeating elementary steps, each of which has a chain carrier. Once started, chain reactions continue until the reactants are exhausted. Fire and explosions are some of the phenomena associated with chain reactions. The chain carriers are some intermediates that appear in the repeating elementary steps. These are usually free radicals.
    • 15.5: A Catalyst Affects the Mechanism and Activation Energy
      Homogeneous catalysis refers to reactions in which the catalyst is in solution with at least one of the reactants whereas heterogeneous catalysis refers to reactions in which the catalyst is present in a different phase, usually as a solid, than the reactants.
    • 15.6: The Michaelis-Menten Mechanism for Enzyme Catalysis
      Leonor Michaelis and Maude Menten proposed the following reaction mechanism for enzymatic reactions.  In the first step, the substrate binds to the active site of the enzyme. In the second step, the substrate is converted into the product and released from the substrate.