3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc

• Chemical equilibrium is a dynamic situation which is characterised by:

  > The forward and backwards reaction occurring at the same rate

  > the concentrations of all reactants and products remaining constant

  This can only occur in a closed system
• At dynamic equilibrium both the forward and backwards reactions are happening at the same rate and the concentration of reactants and products stay constant
• Pressure

  Increasing pressure causes the position of equilibrium to move to the side with the least number of moles. This is because equilibrium move to oppose the increase in pressure.

  Rate

  Increasing pressure increases the rate of reaction/ attainment of equilibrium. This is because the particles are closer together. This means there is a greater chance of successful collisions per unit time between particles.
• Catalysts speed up the rate of both the forward and backwards reaction by the same amount

  They reduce the time taken to reach equilibrium

  Catalysts do not change the position of equilibrium

  A catalyst lowers the activation energy for a reaction and will save energy in the long term and costs will go down.
• Kc

  Concentration, Pressure and catalysts do not change the value of kc

  only temperature affects kc if equilibrium moves to the right temperature increases