A chemist proposes the following three-step mechanism for the decomposition of compound X in aqueous solution at 25 °C.
Step 1 (slow) X + Y → I₁
Step 2 (fast) I₁ + Y → I₂
Step 3 (fast) I₂ → Z + Y
The symbol I represents reaction intermediates, and Z is the final product.
Answer the following questions about the mechanism.
(a) Identify every species that is an intermediate in the mechanism. Provide a brief justification based on the definition of an intermediate.
(b) Describe in detail how the molecularity of the rate-limiting step determines the overall rate law for the reaction. Your explanation should reference collision-frequency arguments and the information given in the mechanism.
(c) If a student incorrectly includes both I₁ and I₂ in the proposed rate law, explain why this form of the rate law would be inconsistent with experimental observations.