Which of the following correctly labels the features of an energy diagram for a two-step reaction?

• A. Two transition states, one intermediate, and two activation energies
• B. One transition state, no intermediates, and two activation energies
• C. Two transition states, no intermediates, and one activation energy
• D. One transition state, two intermediates, and one activation energy

Answer: (A)

Verified step by step guidance

1. Understand that an energy diagram for a two-step reaction typically shows the progress of the reaction on the x-axis and the potential energy on the y-axis.
2. Recognize that each step in a reaction mechanism has its own transition state, which appears as a peak on the energy diagram representing the highest energy point for that step.
3. Identify that between two transition states, there is usually an intermediate, which is a species formed during the reaction that has a local energy minimum on the diagram.
4. Note that each step has its own activation energy, which is the energy difference between the reactants (or intermediate) and the transition state for that step.
5. Conclude that for a two-step reaction, the energy diagram should have two transition states (two peaks), one intermediate (one valley between the peaks), and two activation energies (one for each step).