Le Chateliers Principle

Le Chateliers principle states that any change in a system at equilibrium results in a shift of the equilibrium in the direction which minimises the change. The law was originally applied only to pressure and was first published in a note as:

Any system in stable chemical equilibrium, subjected to the influence of an external cause which tends to change either its temperature or its condensation (pressure, concentration, number of molecules in unit volume), either as a whole or in some of its parts, can only undergo such internal modifications as would, if produced alone, bring about a change of temperature or of condensation of opposite sign to that resulting from the external cause.

A good example of the law is the Haber Process Chemical Equation, a reaction that Le Chatelier worked on but subsequently abandoned. The project was continued by Haber and Claude who successfully produced Ammonia on a commercial scale using this process.

N2 (g) + 3H2 (g) <===> 2NH3 (g) + heat

Increasing H2 in system shifts equilibrium to right
Decrease NH3 to shifts equilibrium to the right
Increase Heat to shifts equilibrium to the left


Further info:

The Woodrow Wilson National Fellowship Foundation - Le Chateliers Principle -
http://www.woodrow.org/teachers/ci/1992/LeChatelier.html