Reaction mechanism

Definition

A reaction mechanism describes the step-by-step sequence of elementary reactions by which overall chemical change occurs. It provides detailed information on the intermediates, transition states, and energy changes throughout the process.

5 Must Know Facts For Your Next Test

1. Each elementary step in a reaction mechanism has its own rate law and molecularity.
2. The slowest elementary step is known as the rate-determining step and controls the overall reaction rate.
3. Intermediates are species that appear in the reaction mechanism but not in the overall balanced equation.
4. Catalysts appear in early steps of a reaction mechanism and are regenerated in later steps.
5. The sum of the elementary steps must give the overall balanced equation for the chemical reaction.

Review Questions

• What is an intermediate, and how does it differ from a reactant or product?
• How does the rate-determining step influence the overall reaction rate?
• Explain why catalysts do not appear in the overall balanced equation despite being involved in the mechanism.

Related terms

Elementary Reaction:

A single-step process with a specific molecularity that describes collisions between reactants leading to products.

Rate-Determining Step:

The slowest step in a multi-step reaction mechanism which dictates the overall reaction rate.

Transition State:

A high-energy state during a chemical reaction where bonds are partially formed and broken; represents an energy maximum along the reaction path.