The Effect of Changing Conditions on Equilibrium (AQA GCSE Chemistry: Combined Science)
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Le Chatelier's Principle
- 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 or 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 the 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 and 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 and there is an increase in the amount of reactants formed
Exam Tip
You do not need to learn Le Chatelier's Principle for an exam but you do need to make qualitative predictions about the effect of changes on systems at equilibrium when given appropriate information.
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