5.6.A—Represent the activation energy and overall energy change in an elementary reaction using a reaction energy…

Represent the activation energy and overall energy change in an elementary reaction using a reaction energy profile.

• Elementary reactions typically involve the breaking of some bonds and the forming of new ones.
• The reaction coordinate is the axis along which the complex set of motions involved in rearranging reactants to form products can be plotted.
• The energy profile gives the energy along the reaction coordinate, which typically proceeds from reactants, through a transition state, to products. The energy difference between the reactants and the transition state is the activation energy for the forward reaction.
• The rate of an elementary reaction is temperature dependent because the proportion of particle collisions that are energetic enough to reach the transition state varies with temperature. The Arrhenius equation relates the temperature dependence of the rate of an elementary reaction to the activation energy needed by molecular collisions to reach the transition state.
  • Exclusion: Calculations involving the Arrhenius equation will not be assessed on the AP Exam.