IB Chemistry MPHS
Name:
Date:
Exploring Equilibrium using an Applet
Go to the Equilibrium Applet at http://chemconnections.org/Java/equilibrium/index.html.
The applet shows a reversible reaction between 2 red molecules to form 1 blue molecules. The reaction
can be represented by the following equations:
𝐑 + 𝐑 ⇌ 𝐁
or
𝟐𝐑 ⇌ 𝐁
where R = red molecule and B = blue molecule.
Procedure
Part A: Observing an Equilibrium
1. Set the following parameters:
# red molecules = 30
Probability = 0.25
Temperature = 10 K
# blue molecules = 0
probability = 0.25
2. Click equilibrate.
3. Follow one red molecule around the box. Describe what happens to it over time.
4. Follow one blue molecule around the box. Describe what happens to it over time

Do your observations support the statement that this is a reversible reaction? Explain.
5. Watch the simulation until the number of molecules remains constant. Record the number of each
molecule below.
Number of red = __________
Number of blue= _____________
IB Chemistry MPHS
At this point, the system is said to be in a state of equilibrium. At equilibrium, the concentration of each
substance in the reaction remains constant over time.

Are the number of red and blue molecules equal at equilibrium? _______ If not, which species is
favored at equilibrium?
6. With the simulation running at equilibrium, look carefully at the molecules in the box and record your
observations of any changes that are taking place.

How do your observations support the statement that chemical equilibrium is dynamic?
Part B: Graphs of Chemical Systems at Equilibrium
1. Restart the simulation using the same parameters as Part A. This time, record the number of red
molecules and number of blue molecules every 10 seconds for 2 minutes. You may need a partner to
keep time for you.
Time
0
10
20
30
40
50
60
70
80
90
100
110
120
# red
# blue
IB Chemistry MPHS
2. Construct a line graph of your data below or construct one using Excel and insert it below.
Part C: The Effect of Starting Concentrations on Equilibrium
1. Reset the parameters to the values for Part A, but change the number of molecules to the following:
# red molecules = 0
# blue molecules = 15
2. Click equilibrate.
3. Time how long it takes for the system to reach equilibrium. Record the composition of the reaction
mixture at equilibrium.
IB Chemistry MPHS
4. Reset the parameters to the values for Part A, but change the number of molecules to the following:
# red molecules = 12
# blue molecules = 9
5. Click equilibrate.
6. Time how long it takes for the system to reach equilibrium. Record the composition of the reaction
mixture at equilibrium.
7. You have now let the system reach equilibrium from three different starting concentrations.
Condition #1
Condition #2
Condition #3

# red initial
30
0
12
# blue initial
0
15
9
What relationship did you see between the # of each molecule at the start and
a) the equilibrium composition (i.e. the # of each molecule when equilibrium was reached)?
b) time it took for equilibrium to be reached?
8. Other reaction conditions may influence a chemical equilibrium. What conditions were not
investigated in this activity?