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

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