Chemical Equilibrium in Lab Experiments

At the start of the lab, the "Reactants" cylinder contained 50 mL of water, and the "Products" cylinder was empty. After several transfers, the volumes stabilized. What do you notice about the final volumes in each cylinder? Are they equal? Why or why not?

Answer explanation

1. The final volumes are not equal (e.g., 20 mL in "Reactants" and 30 mL in "Products"). This happens because the straws have different sizes, so the amount of water transferred in each direction isn’t the same, even though the process balances out at equilibrium. Equal volumes aren’t required for equilibrium—just equal transfer rates.

When did you first observe that the volumes in the "Reactants" and "Products" cylinders stopped changing significantly? What does this stabilization represent in terms of a chemical equilibrium?

Answer explanation

1.  The volumes likely stopped changing significantly around transfer #8 or #10 (depending on data). This stabilization represents chemical equilibrium, where the forward and reverse "reactions" (transfers) happen at the same rate, so there’s no net change in the amounts.

In this lab, water is transferred back and forth between the cylinders, even after the volumes stabilize. How does this continuous transfer demonstrate that chemical equilibrium is a dynamic process?

Answer explanation

1. The continuous transfer shows that even at equilibrium, the "forward" and "reverse" processes keep happening, just like in a chemical reaction where reactants turn into products and back again at equal rates. It’s dynamic because the system is active, not static.

In a chemical equilibrium, the amounts of reactants and products don’t necessarily have to be equal. How does this lab activity support that idea? Use your final volume measurements to explain.

Answer explanation

4. The lab supports this because the final volumes aren’t equal (e.g., 20 mL in "Reactants" and 30 mL in "Products"). Equilibrium is about the rates of transfer balancing, not the amounts being the same, just like in a chemical reaction where the equilibrium constant determines the ratio, not equality.

The lab uses a smaller straw for the forward "reaction" and a larger straw for the reverse "reaction." How does this difference affect the final volumes in the "Reactants" and "Products" cylinders at equilibrium? What does this suggest about the equilibrium position in a real chemical system?

Answer explanation

4. The larger straw moves more water back to "Reactants," so "Products" ends up with more water (e.g., 30 mL vs. 20 mL). This suggests that in a real chemical system, the equilibrium position depends on the relative strengths of the forward and reverse processes, shifting toward the side favored by the stronger "reaction."

Suppose you added an extra 20 mL of water to the "Reactants" cylinder after equilibrium was reached. Predict how the system would respond to restore equilibrium. Would the final volumes change? Explain using Le Châtelier’s Principle.

Answer explanation

7. Adding 20 mL to "Reactants" increases its volume (e.g., from 20 mL to 40 mL). Per Le Châtelier’s Principle, the system shifts toward "Products" to reduce the extra "reactants." More water would transfer to "Products," so both final volumes would increase (e.g., to 25 mL and 35 mL), but the ratio would stabilize again.

If you removed 10 mL of water from the "Products" cylinder after equilibrium was established, how would the system adjust? Describe the shift in equilibrium and why it occurs, referencing Le Châtelier’s Principle.

Answer explanation

7. Removing 10 mL from "Products" (e.g., from 30 mL to 20 mL) decreases its volume. Le Châtelier’s Principle says the system shifts toward "Products" to replace what was lost. Water would move from "Reactants" to "Products," lowering "Reactants" (e.g., to 15 mL) and raising "Products" (e.g., to 25 mL) until equilibrium is restored.

In a real chemical system, increasing the concentration of a reactant shifts the equilibrium toward the products. How could you simulate this in the lab? What would you expect to see in the volumes of the "Reactants" and "Products" cylinders afterward?

Answer explanation

7. You could simulate this by adding water to the "Reactants" cylinder (e.g., 20 mL). The system would shift toward "Products," so "Reactants" volume would decrease from its new total, and "Products" volume would increase (e.g., from 30 mL to more), settling at new higher volumes with a similar ratio.

If you repeated the lab using two straws of the same size, how would the final volumes in the "Reactants" and "Products" cylinders compare to your original results? What does this tell you about the role of "transfer capacity" in reaching equilibrium?

Answer explanation

10. With equal straw sizes, the final volumes would be equal (e.g., 25 mL each). This differs from the original unequal volumes (20 mL and 30 mL). It shows that "transfer capacity" (straw size) determines the equilibrium position—equal capacities balance the amounts, while unequal ones favor one side.

In this lab, the total volume of water (50 mL) stays constant. How is this similar to the conservation of mass in a closed chemical system at equilibrium?

Answer explanation

10. The total 50 mL doesn’t change, just like in a closed chemical system where mass is conserved. The atoms (or water) shift between reactants and products, but the total amount stays the same, reflecting how equilibrium redistributes matter without losing it.