An energy diagram for a chemical reaction shows seven distinct regions (bins) labeled as follows: (1) Reactants, (2) Activation energy, (3) Transition state, (4) Intermediate, (5) Second activation energy, (6) Second transition state, (7) Products. Which type of reaction does this energy diagram most likely represent?

• A. A single-step exothermic reaction
• B. A two-step reaction with an intermediate
• C. A single-step endothermic reaction
• D. A decomposition reaction with no intermediate

Answer: (B)

Verified step by step guidance

1. Identify the key features of the energy diagram: it shows two activation energy regions and two transition states, separated by an intermediate region.
2. Recall that a single-step reaction typically has only one activation energy peak and one transition state, without any intermediate.
3. Understand that the presence of an intermediate indicates the reaction proceeds through multiple steps, with the intermediate being a species formed and consumed during the reaction.
4. Recognize that two activation energies and two transition states correspond to a two-step reaction mechanism, where each step has its own energy barrier and transition state.
5. Conclude that the energy diagram most likely represents a two-step reaction with an intermediate, rather than a single-step or decomposition reaction without intermediates.