AQA AS Chemistry Unit 2: Equilibrium


Chemistry Unit 2: Equilibria

The Idea of Equilibrium

  • Equilibrium mixture: The mixture formed when a reversible reaction proceeds in a closed container until no further change occurs. The backward and forward reactions are proceeding at the same rate

Setting up an Equilibrium

  • Dynamic Equilibrium: Forward and Backward reactions are occurring at the same rate so the mixture composition doesn't change


  • Can only be reached in a closed system

  • The final equilibrium position will be the same

  • It is a dynamic process where the forwards and backwards reactions occur at the same time

  • When the density, concentration, colour and pressure are the same equilibrium has been reached

Chemical Equilibria

  • Equilibrium can be formed of any proportions of reactant and products

Proportions can change due to conditions like temperature, pressure and


Changing Conditions

The Equilibrium Mixture

  • Changing the proportions of reactants to products is a way of being able to obtain a greater yield of product

  • This is changing the position of equilibrium

  • If the proportion of product is increased the equilibrium position shifts to the right

  • If the proportion of reactants is increased the equilibrium position shifts to the left

Le Chatelier's Principle

If a system at equilibrium is disturbed, the equilibrium position moves to oppose it

Changing Concentrations

  • If you increase the concentration of a reactant then the equilibrium position shifts to reduce this concentration

  • The equilibrium position moves to the right increasing the yield of product

Temperature Increase

  • Equilibrium


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