# Le Chateliers Principle

## Le Chateliers Principle

#### Introduction

Le Chateliers principle states:

The position of the equilibrium of a system changes to minimise the effect of any imposed change in conditions.

This principle applies to any reaction that is in equilibrium.

#### The effect of concentration changes on equilibrium

Changing concentration of a reactant or product does not change the numerical value of the equilibrium constant, but it does change the position of the equilibrium.

In general, the position of the equilibrium is shifted towards the right if the concentration of a reactant is increased or to the left if the concentration of a product is increased.

At the start, when the change is made, the mixture is not at equilibrium, but equilibrium is eventually restored.

#### The effect of pressure changes on equilibrium

For a reaction involving gases, altering the pressure may cause a change in the position of the equilibrium.

For a reaction where there is an increase in the number of moles from reactants to products, increasing the pressure moves the equilibrium to the left.

Where there is a decrease in the number of moles from reactants to products, increasing the pressure moves the equilibrium to the right. The equilibrium constant remains the same.

#### The effect of temperature changes on equilibrium

The change that takes place when temperature is changed depends upon whether the forward reaction is exothermic or endothermic.

If the forward reaction is exothermic then the backward one is endothermic.

If the temperature is increased, the equilibrium moves to the left, since an endothermic reaction will tend to reduce the temperature.

Conversely, if the temperature is decreased then the equilibrium, moves to the right.

#### The effects of catalysts on equilibrium

A catalyst has no effect on the position of the equilibrium. However, it does increase the rate of both the forward and backward reactions, decreasing the time taken to reach equilibrium.