LeChâtelier’s Principle

Learning Objectives

  • State Le Châtelier’s principle.

How far down?

There are people who enjoy going up in an airplane, strapping on a parachute, and diving out the door to free-fall and then open the chute and drop to the ground. This stressful activity (so they say) relieves the stress of everyday life. The release of adrenaline caused by this stressful behavior is said to promote a mood enhancement that helps you deal better with other stresses in your daily life.

Skydiving adds stress like LeChatelier's principle

Le Châtelier’s Principle

Chemical equilibrium was studied by French chemist Henri Le Châtelier (1850–1936) and his description of how a system responds to a stress to equilibrium has become known as Le Châtelier’s principle: When a chemical system that is at equilibrium is disturbed by a stress, the system will respond in order to relieve the stress.

Henri LeChatelier postulated that a chemical system moves to release stress from the system

Figure 1. Henri Le Châtelier

Stresses to a chemical system involve changes in the concentration of reactants or products, changes in the temperature of the system, or changes in the pressure of the system. We will discuss each of these stresses separately. The change to the equilibrium position in every case is either a favoring of the forward reaction or a favoring of the reverse reaction. When the forward reaction is favored, the concentrations of products increases, while the concentrations of reactants decreases. When the reverse reaction is favored, the concentrations of products decreases, while the concentrations of reactants increases.

Original Equilibrium Favored Reaction Result
A rightleftarrows B forward: A rightarrow B [A] decreases; [B] increases
A rightleftarrows B reverse: A leftarrow B

[A] increases; [B] decreases

Summary

  • Le Châtelier’s principle describes how a reaction system at equilibrium is influenced by stress.

Practice

Read Le Châtelier’s biography and answer the following questions.

  1. Who gave him his early training in math and chemistry?
  2. What was his first area of investigation?
  3. What was another area of interest?
  4. When did he first propose his principle?

Review

  1. What does Le Châtelier’s principle state?
  2. If the forward reaction is favored in the equilibrium, what will increase?
  3. If the reverse reaction is favored in the equilibrium, what will increase?

Glossary

  • Le Châtelier’s principle: When a chemical system that is at equilibrium is disturbed by a stress, the system will respond in order to relieve the stress.