Le Chatelier's principle

(physics) The principle that when an external force is applied to a system at equilibrium, the system adjusts so as to minimize the effect of the applied force.

A description of the response of a system in equilibrium to a change in one of the variables determining the equilibrium.

For any chemical reaction equilibrium or phase equilibrium, an increase in temperature at constant pressure shifts the equilibrium in the direction in which heat is absorbed by the system. See also Chemical equilibrium; Phase equilibrium.

For any reaction equilibrium or phase equilibrium, an increase in pressure at constant temperature shifts the equilibrium in the direction in which the volume of the system decreases.

For a reaction equilibrium in a dilute solution, addition of a small amount of a solute species that participates in the reaction will shift the equilibrium in the direction that uses up some of the added solute.

For an ideal-gas reaction equilibrium, addition at constant temperature and volume of a species that participates in the reaction will shift the equilibrium in the direction that consumes some of the added species. For an ideal-gas reaction equilibrium, addition at constant temperature and pressure of a species that participates in the reaction might shift the equilibrium to produce more of the added species or might shift the equilibrium to use up some of the added species; the direction of the shift depends on the reaction, on which species is added, and on the initial composition of the equilibrium mixture.

The noun has one meaning:

Meaning #1: the principle that if any change is imposed on a system that is in equilibrium then the system tends to adjust to a new equilibrium counteracting the change
  Synonyms: Le Chatelier's law, Le Chatelier principle, Le Chatelier-Braun principle