Reaction Mechanisms

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Reaction Mechanisms
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Reaction Mechanisms

• a series of simple steps that lead from the
  initial reactants to the final products of a
  reaction.
• The mechanism must be consistent with the
  stoichiometry of the overall or net reaction.

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Reaction Mechanisms

• The rate-determining step is the crucial step in
  establishing the rate of the overall reaction.
• It is the slowest step that effects the overall
  rate of the reaction.
• In a relay race, you can only be as fast as your
  slowest runner.

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Mechanism for the decomposition of hydrogen
peroxide by a catalyst

• Slow step H2O2 I- ? H2O OI-
• Fast step H2O2 OI- ? H2O O2 I-
• __________________________________________________
  ________
• Net equation 2 H2O2 ? 2 H2O O2

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Catalyst

• Something that is used to make a reaction occur
  more quickly, but is not used up.
• You can recognize a catalyst as something that is
  originally a reactant in one step, then
  regenerates itself as a product later on in the
  mechanism.
• Example I- from previous mechanism.

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Intermediate

• A temporary species that is created during one of
  the steps in a mechanism.
• It is created as a product in one step, then
  later consumed as a reactant in a following step.
  
• It is NOT a part of the overall reaction, but
  used to explain how an overall reaction occurs.
• Example OI- from previous mechanism

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Practice Together.

• Use the mechanism below to answer the following
  questions.
• What is the overall reaction?
• State any intermediates and/or catalysts
• What is the rate determining step?