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LeChateliers Principle

Introduces LeChâtelier’s Principle and how it governs chemical equilibria.

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LeChâtelier's Principle

Skydiving adds stress like LeChatelier's principle

Credit: Courtesy of the US Marine Corps
Source: http://commons.wikimedia.org/wiki/File:USMC-101116-M-3816G-001.jpg
License: CC BY-NC 3.0

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.

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. 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
forward: [A] decreases; [B] increases

[A] increases; [B] decreases

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

Source: http://commons.wikimedia.org/wiki/File:Lechatelier.jpg
License: CC BY-NC 3.0

Henri Le Châtelier [Figure2]


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



Read Le Châtelier’s biography at the link below 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?



  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?

Image Attributions

  1. [1]^ Credit: Courtesy of the US Marine Corps; Source: http://commons.wikimedia.org/wiki/File:USMC-101116-M-3816G-001.jpg; License: CC BY-NC 3.0
  2. [2]^ Source: http://commons.wikimedia.org/wiki/File:Lechatelier.jpg; License: CC BY-NC 3.0

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