Chemical Equilibria

• Dynamic Equilibrium 


  When the forward and backwards rate of reaction is the same and remains at a constant rate. At this point, the concentrations of the reactants and products are constant and appear not to change. It can only occur in closed systems
• Le Chatelier's Principle


  When a system is subject to change, the system will alter to lessen the effect of that change.

  Reaction conditions can be altered to maximise the yield of a desired product
• Changing Temperature 


  Increasing the temperature favours the endothermic reaction and therefore increase the yield of the endothermic products.

  Decreasing the temperature favours the exothermic reaction and the yield of the exothermic products will be increased
• Changing Pressure 


  Increasing the pressure favours the side with fewer moles (equilibrium moves to the side with fewer moles). It will increase the yield of products on this side of the reaction.

  Decreasing pressure favours the side of the reaction with more moles (equilibrium moves to the side with more moles). It will increase the yield of products on this side of the reaction
• Catalysts do not affect the equilibrium position as they affect the forward and backward reaction equally. However, it does allow equilibrium to be reached faster
• Kc indicates the position of equilibrium for a reaction at a certain temperature. Kc for a reaction always has the same value unless the reaction conditions and therefore the position of equilibrium is changed
• The value of Kc is not affected by concentration change or use of a catalyst, however it is affected by changing the reaction temperature
• Increasing the temperature of an endothermic reaction would increase the value of Kc.

  Decreasing the temperature of an endothermic reaction would decrease the value of Kc
• Increasing the temperature of an exothermic reaction would decrease the value of Kc.

  Decreasing the temperature of an exothermic reaction would increase the value of Kc.