Enduring Understanding 4.B.2: Boltzmann & Arrhenius

  • To overcome the energy barrier of a reaction, a particle must have sufficient energy.
  • Reaction mixtures contain a very large number of particles with differing amounts of energy.
  • The distribution of energies of particles can be described by the Maxwell-Boltzmann thermal distribution of particle energies. This is illustrated in the following graphic:

  • There are two curves on the graph, one representing a sample of reactant gas molecules at a temperature of 300 K, and the other the same sample at a temperature of 400 K.
  • There is also an activation energy threshold of a reaction, Eact, indicated.
  • Molecules with energy above Eact will have sufficient energy to undergo a reaction. As the graph shows, there are more molecules above Eact at 400 K than at 300 K, therefore the reaction will occur more rapidly at the higher temperature

  • The Arrhenius equation is a mathematical function that gives the rate of a reaction, as a function of the activation energy Ea and the temperature T.
  • K = Ae-Ea/RT

  • A and R are constants.

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