Problem 3 - Chemistry A Guided Inquiry

Question

How does the rate of the rate-limiting step in a mechanism involving a catalyst compare to the rate of the rate-limiting step of the mechanism without the catalyst present? Explain your reasoning.

Step-by-Step Solution

Answer

The rate of the rate-limiting step in a reaction mechanism is faster when a catalyst is present compared to when the catalyst is absent. This is because a catalyst provides an alternative reaction pathway with a lower activation energy, thus speeding up the rate-limiting step.

Step 1: Understanding the Role of a Catalyst

A catalyst is a substance that increases the rate of a chemical reaction by providing an alternative reaction pathway with a lower activation energy. It does not alter the products of the reaction nor is consumed in the reaction, which means it can be used multiple times.

Step 2: Understanding The Rate-Limiting Step

The rate-limiting step in a reaction mechanism is the slowest step. This is the step that determines the overall rate of the reaction since it takes the longest time to complete.

Step 3: Comparing the Rate of the Rate Limiting Step with and without a Catalyst

When a catalyst is introduced into a reaction, it provides an alternative pathway with a lower activation energy for the reaction to take place. This lowers the energy barrier for the rate-limiting step, allowing it to proceed more quickly. Consequently, the rate of the rate-limiting step in a mechanism involving a catalyst is faster compared to the rate of the rate-limiting step of the mechanism without the catalyst present.