Which of the following statements is true about the rate-determining step of a reaction mechanism?
It is the fastest step in the mechanism
It is the slowest step in the mechanism
It has the highest concentration of reactants
It determines the overall equilibrium constant of the reaction
The correct answer and explanation is:
The correct answer is: It is the slowest step in the mechanism.
Explanation:
In a multi-step chemical reaction, the rate-determining step (RDS) is the slowest step in the reaction mechanism. This step controls the overall rate of the reaction, as the reaction cannot proceed any faster than the slowest step. It acts as a bottleneck for the reaction, meaning that all subsequent steps must wait for it to be completed before proceeding.
Here’s a deeper look into the other options:
- It is the fastest step in the mechanism: This statement is incorrect. The fastest step would not be the rate-determining step; it would be the one that does not limit the overall speed of the reaction.
- It has the highest concentration of reactants: This statement is not necessarily true. The concentration of reactants is important in determining the rate of the reaction, but the rate-determining step is based on how fast the individual steps proceed, not on the concentration of reactants.
- It determines the overall equilibrium constant of the reaction: The equilibrium constant is determined by the overall reaction and the balance between the reactants and products at equilibrium. The rate-determining step does not directly affect the equilibrium constant.
The rate-determining step is significant because it essentially limits how fast the entire reaction can proceed, regardless of the speed of the other steps. It is crucial for understanding the kinetics of the reaction and for predicting how changes in conditions like temperature or concentration will affect the rate of the reaction.