Exploring Equilibrium Honors Chemistry
Name:______Date: ______
Purpose: To illustrate the experimental conditions necessary to have a system at equilibrium.
Materials: 48 pennies
Part I:
Procedure:
1. Fold a piece of paper in half, and label one side A and the other side B.
2. Place the 48 pennies in a pile on side A.
3. You will now model a chemical reaction coming to dynamic equilibrium by moving the pennies from pile to pile according to certain rules. These rules are called rate constants, and in this reaction the rate constants will tell you how many pennies to move from pile A to pile B, and from pile B to pile A. When you move pennies between piles, you will make the exchange at the same time.
- Rate constant A à B = ½ per round
- Rate constant B à A = ¼ per round
4. Following the rules set by the rate constants, move the appropriate number of pennies from pile to pile for a total of ten rounds. Fill in your data on the table below. If you perform a calculation that results in a fraction of a penny, round down. The first two rounds have been filled in so that you get the idea.
Part I Round # / Pennies in A at start / Pennies in B at start / # Pennies moved Aà B / # Pennies moved Bà A / Total # pennies1 / 48 / 0 / 24 / 0 / 48
2 / 24 / 24 / 12 / 6 / 48
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Part II: Different Rate Constants
Procedure:
1. Fold a piece of paper in half, and label one side A and the other side B.
2. Place the 48 small pennies in a pile on side A.
3. You will now model a chemical reaction coming to dynamic equilibrium by moving the pennies from pile to pile according to certain rules. These rules are called rate constants, and in this reaction the rate constants will tell you how many pennies to move from pile A to pile B, and from pile B to pile A. When you move pennies between piles, you will make the exchange at the same time.
- Rate constant A à B = ¼ per round
- Rate constant B à A = ½ per round
4. Following the rules set by the rate constants, move the appropriate number of pennies from pile to pile for a total of ten rounds. Fill in your data on the table below. If you perform a calculation that results in a fraction of a penny, round down. The first two rounds have been filled in so that you get the idea.
Part II Round # / Pennies in A at start / Pennies in B at start / # Pennies moved Aà B / # Pennies moved Bà A / Total # Pennies1 / 48 / 0 / 12 / 0 / 48
2 / 36 / 12 / 9 / 6 / 48
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Data Analysis: Hold your graph paper lengthwise and divide it in two. Construct two graphs with number of pennies in A and B on the y-axis and the round number on the x-axis. Connect the points so that there is one line in each graph for A and another for B. Use a different color for each.
Conclusion Questions:
1. Describe what happened to the size of piles A and B over the course of the nine rounds.
2. Describe how you knew that equilibrium was established based on:
a) the data for the number of pennies on the table
b) the plotted data on the graph
3. Explain in your own words why the size of the piles eventually became constant.
4. How is the relationship between the final size of pile A and pile B different between Part II and Part I? Explain why this is.
When a chemical reaction (for us, Aà B or Bà A) reaches a state of dynamic equilibrium, the ratio of the products (B) to reactants (A) will always be the same. This ratio is called the equilibrium constant, Keq.
5. Calculate Keq for both Part I & Part II, assuming that the number of pennies is their concentration. Does that mean that products or reactants are favored for each part? Does that agree with your data?
6. Even though the piles started out with the same number of pennies, Parts I & II ended up with different amounts in the piles when they had reached equilibrium. Why is this?
7. Describe what information you would need to calculate Keq for an actual chemical reaction.
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