The Effect of Changing Conditions on Equilibrium (AQA GCSE Chemistry)

Le Chatelier's principle

Higher tier only

• The relative amounts of all the reactants and products at equilibrium depend on the conditions of the reaction

• This balance is framed in an important concept known as Le Chatelier's Principle,

  • Named after Henri Le Chatelier, who was a French military engineer in the 19th century

• This principle states that when a change is made to the conditions of a system at equilibrium, the system automatically moves to oppose the change

• The principle is used to predict changes to the position of equilibrium when there are changes in:

  • Temperature

  • Pressure 

  • Concentration

• Knowing the energy changes, states and concentrations involved allows us to use the principle to manipulate the outcome of reversible reactions

• For example, if pressure is increased, the position of equilibrium moves in the direction which has the smallest amount of gaseous molecules

• The position of equilibrium is said to shift to the right when the forward reaction is favoured

  • This means that there is an increase in the amount of products formed

• The position of equilibrium is said to shift to the left when the reverse reaction is favoured

  • So, there is an increase in the amount of reactants formed