Name______________________________________________Date___________________
Equilibrium Straw Activity
Problem: How can you tell when a system is at equilibrium?
Materials:
 25 mL graduated cylinders (2) or 10 mL graduated cylinders
 2 drinking straws with different diameters
 Graph paper
Procedure:
1. Label one graduated cylinder “Reactants” and the other “Products.” Label the straw with the larger diameter
the “Forward” straw and the other with the smaller diameter “Reverse.”
2. Fill the reactant cylinder with water to the 25.0 mL/10 mL mark.
3. Place the forward straw (larger diameter) in the reactant cylinder. Place the reverse straw (smaller diameter)
in the product cylinder.
4. Be sure the straw is resting on the bottom. Put your finger over the top of the forward straw. Transfer the
water to the products cylinder. Be sure not to “lose” any water from the straw during the transfer.
5. Now put your finger over the top of the reverse straw and transfer water from the products cylinder to the
reactants cylinder.
6. Record the volume in each cylinder in your data table for Experiment 1. Each time you transfer liquid from the
reactant cylinder to the product cylinder and back from the product cylinder to the reactant cylinder
constitutes one transfer.
7. Repeat Steps 5, 6, and 7 until the volumes in the cylinders REMAIN CONSTANT for at least 5 readings.
Remember constant volumes does not mean equal volumes.
8. Repeat the entire experiment, (Experiment 2) starting with 25.0 mL/10 mL of water in product cylinder and
nothing in the reactant cylinder. Make sure the smaller diameter straw is in the products cylinder. It is still
the reverse reaction. Then start transferring water from the products to reactants.
Observations:
1. Did you use the larger straw for the forward or the reverse reaction? (Check procedure)
2. In experiment 1 at equilibrium, was there a greater volume of products or reactants?
3. In experiment 2 at equilibrium, was there a greater volume of products or reactants?
Analysis and Conclusions:
1. Was equilibrium established in both experiments? Explain how you know from your data.
2. Explain how this experiment demonstrated dynamic equilibrium. Be sure to include the definition of dynamic
equilibrium in your explanation.
Data Tables
Exp 1: Forward Reaction
Trial 1
Transfer
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Volume
R (mL)
P (mL)
25/10.0
0.0
Exp 2: Reverse Reaction
Trial 2
Transfer
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Volume
R (mL)
P (mL)
0.0
25/10.0
Graph your results for both trials by plotting the transfer number on the x-axis and the volumes for both
reactants and products on the y-axis for each trial. Draw a smooth curve through your points. (This means
there will be 4 curves on your graph.) Remember to title your graph, label axes, and include a legend.