(a) Can an intermediate appear as a reactant in the first step of a reaction mechanism? (b) On a reaction energy profile diagram, is an intermediate represented as a peak or a valley?

Verified step by step guidance

1. Step 1: Understand what an intermediate is in a reaction mechanism. An intermediate is a species that is formed in one step of a reaction mechanism and consumed in a subsequent step. It is not present in the overall balanced equation for the reaction.
2. Step 2: Consider the role of an intermediate in a reaction mechanism. Since an intermediate is formed during the reaction process, it cannot appear as a reactant in the first step of the mechanism. It must be produced first before it can be consumed.
3. Step 3: Examine a reaction energy profile diagram. This diagram plots the potential energy of the system as the reaction progresses from reactants to products.
4. Step 4: Identify the features of a reaction energy profile diagram. Peaks on the diagram represent transition states, which are high-energy states that occur between reactants and intermediates or intermediates and products.
5. Step 5: Determine where intermediates appear on the energy profile. Intermediates are represented as valleys on the diagram, indicating a lower energy state between two transition states.