Summary

In this activity, students perform a hands-on activity that models chemical equilibrium based on the article Equilibrium: A Teaching/Learning Activity by Audrey H. Wilson from the Journal of Chemical Education, Vol. 75, No. 9, September 1998.

Grade Level

High School

NGSS Alignment

This activity will help prepare your students to meet the performance expectations in the following standards:

• HS-PS1-6: Refine the design of a chemical system by specifying a change in conditions that would produce increased amounts of products at equilibrium.
• Scientific and Engineering Practices:
  • Using Mathematics and Computational Thinking
  • Analyzing and Interpreting Data

AP Chemistry Curriculum Framework

This activity supports the following unit, topics and learning objectives:

• Unit 7: Equilibrium
  • Topic 7.1: Introduction to Equilibrium
    • 7.1.A: Explain the relationship between the occurrence of a reversible chemical or physical process, and the establishment of equilibrium, to experimental observations.
  • Topic 7.4: Calculating the Equilibrium Constant
    • 7.4.A: Calculate Kc or Kp based on experimental observations of concentrations or pressures at equilibrium.
  • Topic 7.7: Calculating Equilibrium Concentrations
    • 7.7.A: Identify the concentrations or partial pressures of chemical species at equilibrium based on the initial conditions and the equilibrium constant.
  • Topic 7.10: Reaction Quotient and Le Châtelier’s Principle
    • 7.10.A: Explain the relationships between Q, K, and the direction in which a reversible reaction will proceed to reach equilibrium.

Objectives

By the end of this lesson, students should be able to:

• Recognize when equilibrium is reached.
• Recognize that at equilibrium the rate of the forward and reverse reactions are equal.
• Recognize that the concentration of products and reactants remain constant at equilibrium.
• Understand that equilibrium can be approached from many starting points and both directions.

Chemistry Topics

This lesson supports students’ understanding of:

• Chemical Equilibrium

Time

Teacher Preparation: 10 minutes

Lesson: 30 minutes

Materials (per group)

• 50 small items, such as toothpicks, matches, or pennies
• Student activity sheet
• Calculator

Safety

• No specific safety precautions need to be observed for this activity.

Teacher Notes

This activity is designed to introduce the concept of chemical equilibrium.

1. Divide students into small groups.
2. Each group should have 50 small items, such as toothpicks, matches, or pennies and an activity sheet.
3. Each group should be further divided into two groups – Reactants and Products.
4. The Reactants and Products should start with the designated number of items and use the designated reaction rate.
5. For each step the Reactants and Products calculate how many of their items will “react” and be transferred to the other side.
   • If the calculated value is equal or greater than --.5, they should round up to the next whole number.
   • If the calculated value is less than --.5, they should round down to the last whole number.
   • The calculated values should be entered into the data table.
   • The two groups will then swap their reacted items.
6. Repeat step 5 until equilibrium is reached.
7. Repeat the process for the values given for Activity 2 and 3.
8. When all groups have finished the activity, students should review their data and answer the follow up questions.
9. Lead a discussion about chemical equilibrium and have students use their data to support their answers.

Note: After the initial activity you may want to have the groups use new initial conditions (concentration and reaction rate) and complete calculations in a new data table instead of using the small items and rounding.

Answer key and student activity sheet are available as a download.