Name_______________________________________________________Period #_________
Exploration of Le Châtelier’s Principle 2013
Le Châtelier’s Principle states that when stress is brought to bear on a system at equilibrium the system will react in the direction that
will relieve the stress. In general, there are 3 things that will “stress” a system at equilibrium. These are changes in concentrations of
chemicals, volume of the container the reaction occurs in, and the temperature at which the reaction occurs.
The following website will allow you to manipulate different variables to further investigate Le Châtelier’s Principle.
http://www.chm.davidson.edu/ChemistryApplets/equilibria/LeChatelier.html
Throughout these explorations you will be using the below equation. It shows the first step in the conversion of coal into gasoline and
is called the steam reforming reaction.
C (s) + H2O (g)
CO (g) + H2 (g)
Suppose that 0.0500 mole each of carbon, water, carbon monoxide, and hydrogen are placed in a 10.0 L glass bulb, which is then
heated to 1000 K and the steam reforming reaction is allowed to reach equilibrium.
Experiment 1 – The Effect of Changing Concentrations:
Perform the following experiments and carefully observe the behavior of the system. As you alter the system, make sure you are
looking at both the graph and the values underneath the slide bars. Sometimes the bar graph does not change, but the
number underneath do.
1a. Use the bottom slider to increase the analytical amount of hydrogen and observe how the equilibrium amounts of each species
change. Obviously the equilibrium amount of hydrogen increases. What happens to the equilibrium amounts of:
Carbon:
Water:
Carbon Monoxide:
1b. Decrease the amount of hydrogen. What happens to the equilibrium amounts of:
Carbon:
Water:
Carbon Monoxide:
1c. Why does the concentration of Carbon Monoxide have to change in the opposite direction as the concentration of Hydrogen?
1d. Increasing or decreasing the amount of hydrogen “stresses” the equilibrium state of the reaction. Therefore, the concentrations of
water and carbon monoxide change to relieve that stress. Look at your answers to questions 1a and 1b and explain why the
concentrations of water and carbon changed (increased/decreased) the way they did.
2a. Reset the experiment. Use the second slider to decrease the analytical amount of water. What happens to the equilibrium amounts
of:
Carbon:
Hydrogen:
Carbon Monoxide:
2b. Explain how the changes in hydrogen and carbon monoxide relieve the “stress” on the equilibrium system caused by the
concentration of water decreasing.
3a. Reset the experiment. Use the top slider to increase the analytical amount of carbon in the system. What happens to the
equilibrium amounts of:
Water
Carbon monoxide
Hydrogen
3b. Carbon is a solid, while the other chemicals are gasses. Think about how you would write an equilibrium expression for this
equation. How does this explain your answer to 3a?
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Name_______________________________________________________Period #_________
4. Reset the experiment. Use the top slider to slowly decrease the analytical amount of carbon in the system. Initially the equilibrium
amounts of the other chemicals do not change. At what amount of carbon do the equilibrium amounts of the other chemicals in the
reaction begin to decrease? Why does this behavior occur? (Hint: Remember this is a reversible chemical reaction.)
Use the arrow at the bottom of the page to go to the next experiment looking at changes in volume.
Experiment 2 – The Effect of Changing Volume
C (s) + H2O (g)
CO (g) + H2 (g)
In this experiment you need to remember two things:
1) Volume of a gas is inversely related to the pressure the gas is under, so if volume is increasing than pressure is
decreasing.
2) Pressure is caused by the collision of the gaseous (not solid) chemicals involved in equilibrium. More collisions equal
more pressure and less collisions equal less pressure.
1a. Reset the experiment. Drag the piston barrier to increase the volume of the system. What happens to the equilibrium amounts of:
Hydrogen:
Carbon monoxide:
Carbon:
Water:
1b: By increasing the volume of the system you have decreased the pressure of the system, which means there are fewer collisions. In
order to overcome this “stress” there needs to be more collisions in the increased space. Look at how the concentrations of each
changes. How do these changes result in more collisions occurring?
2a. Drag the piston barrier to decrease the volume of the system. What happens to the equilibrium amounts of:
Hydrogen:
Carbon monoxide:
Carbon:
Water:
2b. How do these changes reduce the “stress” on the equilibrium system that occurred when the volume was decreased?
Use the arrow at the bottom of the page to go to the next experiment looking at changes in temperature.
Experiment 3 – The Effect of Changing Temperature
For this experiment we will be using the following reaction:
Heat + C (s) + H2O (g)
CO (g) + H2 (g)
1. If heat is written as a reactant in a reaction, does that mean the reaction is endothermic or exothermic? Explain your answer.
2a. Reset the experiment. Use the slider to increase the temperature of the system. What happens to the equilibrium amounts of:
Hydrogen:
Carbon monoxide:
Carbon:
Water:
2b. Reset the experiment. Use the slider to decrease the temperature of the system. What happens to the equilibrium amounts of:
Hydrogen:
Carbon monoxide:
Carbon:
Water:
3. Explain how the changes in concentrations that result in question 2, release the “stress” caused on the equilibrium system due to
increasing or decreasing of the temperature.
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