Problem 148 - Introductory Chemistry Atoms First

Question

What is meant by the term rate-determining step?

Step-by-Step Solution

Answer

The term "rate-determining step" refers to the slowest step in a chemical reaction mechanism, which ultimately determines the overall rate of the reaction. It is crucial for studying reaction kinetics, as it helps scientists understand which factors affect the overall rate of the reaction and develop strategies to speed it up. For example, in a hypothetical reaction with three steps (fast, slow, and fast), the slow step is the rate-determining step and will set the overall reaction rate.

Step 1: Definition

In the context of a chemical reaction or process, the rate-determining step is the slowest step in the reaction mechanism. This step ultimately determines the overall rate of the reaction, because the entire process cannot proceed faster than the slowest individual step.

Step 2: Reaction Mechanism

The reaction mechanism is the sequence of elementary steps, or individual processes, that together describe the overall transformation of reactants into products. Each elementary step may have a different rate, and the rate-determining step is the one with the lowest rate.

Step 3: Importance in Kinetics

Identifying the rate-determining step is crucial for studying the kinetics of a reaction, because it allows scientists to understand which factors affect the overall rate of the reaction. By focusing on the slowest step, researchers can develop strategies to speed up the reaction, such as by changing the temperature, pressure, or concentration of the reactants, or by using a catalyst.

Step 4: Example

Let's consider a hypothetical reaction with the following mechanism: Step 1: A + B → C (fast) Step 2: C + D → E (slow) Step 3: E + F → G (fast) In this reaction, there are three elementary steps. Step 1 is fast, step 2 is slow, and step 3 is fast. Since step 2 has the slowest rate compared to the other steps, it is considered the rate-determining step, and the overall reaction rate will be determined by step 2.