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Exploring Equilibrium

Exploring Equilibrium

Author: carolyn fruin

Learning Targets:

    I can

  • use a physical experiment to model chemical equilibrium
  • describe what is happening at the molecular level as an equilibrium is being reached
  • sketch how the number of reactants and products will change as a reaction proceeds
  • identify on a graph where equilibrium has been reached
  • predict how changing the initial conditions will affect the equilibrium amounts of reactants and products
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Exploring Equilibrium Handout

This is a three part assignment exploring the topic of equilibrium. This handout is a roadmap for you to keep track of the your learning for each activity. They can be done in any order.


Part 1 - Laboratory Simulation

Directions: Read 1-5, make an appropriate data table, and then begin.

  1.   Label the 1000 ml beakers A and B
  2. Put about 700 ml water in the large beaker “A”.  Leave the other beaker “B” empty.
  3. Record the volume of water in the beakers in your table.
  4. Transfer water between the large beakers using the following “rules”
  • Use the 100 mL beaker to transfer water from A to B;
  • Use the 50 mL beaker transfer water from B to A.
  • Fill the small beakers as full as possible without tipping the large beakers in any way.
  • One cycle consists of one A --> B transfer and one B --> A transfer. 
  • For each cycle, record the volume of water in beakers A and B.

       5.  Continue cycles and recording the volumes, until the level of water in beakers A and B are unchanging.


  1. Graph the volumes of water in beakers A and B per cycle. Make sure to place the independent variable on the y-axis. (attach this to the back of this activity).
  2. Describe in your own words how this experiment relates to a chemical reaction equilibrium.
  3. What is the ratio of the volume in Beaker B to Beaker A at equilibrium?                          When we work with chemical experiments, what value do we calculate that is similar? 
  4. What do you think would be different/same if the water transfers were repeated with the beaker A initially half full? 
  5. Test your ideas with the equipment. Explain how your ideas were supported or need to be corrected.
  6. Sketch what you think the graph will look like if you repeated the directions starting with beaker A empty and beaker B with 700ml? Remember that a “cycle” is using the 100ml beaker to take from A and the 50ml beaker to take from B.
  7. Repeat the directions to test your ideas. Explain how your ideas were supported or need to be corrected.
  8. Do initial quantities affect the overall ratio once equilibrium is established? Explain your answer.
  9. Explain the phrase,  "Equilibrium does not mean Equal".

Part 2 - Computer Tutorial

Go to the site "Equilibrium tutorial". View the tutorial while answering the questions on the handout at the bottom of this lesson.

Next, view the "LeChatelier's Principle tutorial". Take any notes that may help you understand the concept.

Source: W. W. Norton & Company

Part 3 - PhET Computer Simulation

Click on PhET Reactions and Rates Simulation

1.  When the simulation is open, click on the Rate Experiments tab. Design experiments and provide evidence to answer the following. 

  • Predict what will happen if 50 A’s are added to 50 BC’s.
  • Type in the above values and begin the experiment.  Record your observations.
  • With the water exchange experiment, Beaker A water represented reactants and Beaker B represented the products; how does this chemical reaction simulation compare to the water reaction in part 1?
  • How do you know when equilibrium has been reached? Do the numbers ever not change? Why?
  • Is this reaction endothermic or exothermic? How do you know?

2.  Explore the simulation by changing the initial amount of A. How does changing the initial amounts of the reactant affect the amount of product? (use several trials for your evidence)

3.  Predict how increasing the initial temperature of the reactants to just below the activation energy will affect the amount of product. Try it and record your results. Again, use several trials to support your conclusions.

4.  Predict how increasing the initial temperature above the activation energy will affect the amount of product. Try it and record your results.

5.  On a separate piece of paper, summarize what you have learned about reversible reactions and a dynamic equilibrium.