Objective: To demonstrate how a knowledge of a rate-determining step preceded by fast equilibrium can help determine the rate law of a reaction mechanism.

Materials: Pencils; paper; colored marker pens; chalkboard or whiteboard; post-it notes

Activity:

1. Ask the students to draw a representation of a reaction mechanism in which the rate-determining step is preceded by a faster equilibrium process on the board.

2. Explain that in order to calculate the rate of the reaction, we need to know how quickly the intermediate forms in the rate-determining process, this is where the equilibrium comes in.

3. Ask the students to write the rate law of the reaction next to the reaction mechanism.

4. Use post-it notes to identify the equilibrium and rate-determining steps.

5. Show the students how to solve the rate law equation and explain why the reaction rate depends on the concentrations of reactants present in the reaction.

6. Have the students use colored markers to color code the reactants in the rate-determining step, the intermediate formed and the products formed. This will help the students to visualize how the rate law equation depends on the concentrations of reactants.

7. Have the students solve several sample problems to practice the concept.

8. Ask the students to explain how this knowledge can help them understand more complicated mechanisms.