Disturbing a System at Equilibrium

This page looks at Le Châtelier's Principle and explains how to apply it to reactions in a state of dynamic equilibrium. Le Châtelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change. If a chemical reaction is at equilibrium and experiences a change such as pressure, temperature, or concentration of products or reactants the equilibrium will shift in the direction to accommodate the change. It covers changes to the position of equilibrium if you change concentration, pressure or temperature and explains very briefly why catalysts have no effect on the position of equilibrium.

Introduction

An action that tends to change the temperature, pressure, or concentrations of reactants in a system at equilibrium stimulates a response that partially offsets the change while a new equilibrium condition is established (2). Hence, Le Châtelier's principle states that any change to a system at equilibrium will adjust to compensate for that change. In 1884 the French chemist and engineer Henry-Louis Le Châtelier proposed one of the central concepts of chemical equilibria, which describes what happens to a system when something briefly removes it from a state of equilibrium.

It is important in understanding that Le Châtelier's Principle is only a useful guide to help you work out what happens when you change the conditions in a reaction in dynamic equilibrium, but it does not explain the microscopic reason for the changes.