Potential energy diagrams Knowledge-Based Download PDF

Questions

1. 1.

   In a potential energy diagram representing a proposed reaction mechanism, which topological feature of the curve directly indicates the total number of elementary steps?

   • A) The number of local minima situated between the initial reactants and the final products
   • B) The difference in potential energy between the highest peak and the initial reactants
   • C) The total number of potential energy peaks (local maxima) along the reaction coordinate
   • D) The overall change in potential energy between the initial reactants and the final products
2. 2.

   In a potential energy diagram representing a multi-step reaction mechanism, which feature identifies the rate-determining step of the overall reaction?

   • A) The elementary step with the most negative enthalpy change
   • B) The elementary step that immediately follows the lowest energy intermediate
   • C) The elementary step possessing the greatest activation energy barrier
   • D) The elementary step that occurs first in the sequence regardless of barrier height
3. 3.

   In a potential energy diagram representing a multi-step reaction mechanism, how is the forward activation energy of the second elementary step defined?

   • A) As the difference in potential energy between the initial reactants and the second transition state
   • B) As the difference in potential energy between the first transition state and the second transition state
   • C) As the difference in potential energy between the reaction intermediate and the second transition state
   • D) As the difference in potential energy between the reaction intermediate and the final products
4. 4.

   In a potential energy diagram representing a multi-step reaction mechanism, which statement correctly describes the chemical entity located at a local minimum between two peaks?

   • A) It is an activated complex containing partially formed bonds that exists only at an energy maximum.
   • B) It is a reaction intermediate that possesses fully formed chemical bonds and a finite lifetime.
   • C) It is a catalyst that lowers the activation energy of both elementary steps without being consumed.
   • D) It is the transition state associated with the rate-determining step of the overall reaction.
5. 5.

   Consider a potential energy diagram for a two-step reaction mechanism where Step 1 is the rate-determining step. Which modification to the diagram is observed upon adding a catalyst that accelerates the overall reaction?

   • A) The activation energy barrier of the first step is reduced, while the net enthalpy change ($\Delta H$) between reactants and products remains identical.
   • B) The potential energy of the reactants is raised, resulting in a smaller overall enthalpy change ($\Delta H$).
   • C) The energy of the reaction intermediate is elevated above the first transition state, eliminating the initial barrier.
   • D) The activation energy barrier of the second step decreases, while the first transition state remains at its original energy level.