AQA GCSE Chemistry

Revision Notes

6.2.4 The Effect of Changing Conditions on Equilibrium

Higher Tier Only

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 Chaterlier’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 temperaturepressure 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

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.

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.

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