Which statement best defines the rate-determining step in a chemical reaction mechanism?

• A. It is the step with the lowest activation energy in the reaction mechanism.
• B. It is the fastest step in the reaction mechanism that determines the product distribution.
• C. It is the slowest step in the reaction mechanism that limits the overall reaction rate.
• D. It is the step where the reactants are first converted into products.

Answer: (C)

Verified step by step guidance

1. Understand that a reaction mechanism consists of multiple elementary steps that together describe the overall reaction.
2. Recognize that the rate-determining step is the slowest step in the mechanism, which controls how fast the overall reaction proceeds.
3. Recall that the slowest step acts as a bottleneck, limiting the overall reaction rate regardless of how fast other steps are.
4. Note that the rate-determining step typically has the highest activation energy, not the lowest, because it requires the most energy to proceed.
5. Conclude that the correct definition of the rate-determining step is: it is the slowest step in the reaction mechanism that limits the overall reaction rate.