10.1.2 Effect of changes in conditions on equilibrium

• Change in concentration [REACTANTS] : If the concentration of reactants is increased, the rate of the forwards reaction increases and so more products form. Since the concentration of products increases, the rate of the backwards reaction also increases, so a new equilibrium is established. This position is further to the right.
• Change in concentration [REACTANTS] : If the concentration of one of the reactants is decreased, the position of equilibrium moves to the left.
• Change in concentration [PRODUCTS] : Increasing the concentration of products will increase the rate of the backward reaction and decrease the rate of the forward reaction. The system reaches a new equilibrium further to the left.
• Effect of changing pressure [ONLY IN A GASEOUS REACTION] : Increasing the pressure of a gaseous mixture may be achieved by reducing the volume of the container or increasing the moles of reactants used (in the same volume). Increasing the pressure favours the side of the reaction with fewer moles of gas, increasing the yield of this side.
• Effect of changing pressure [ONLY IN A GASEOUS REACTION] : Decreasing the pressure of the reaction will favour the side of the reaction with more moles of gas, increasing the yield of this side.
• The effects of a change in pressure can be investigated using a gas syringe and pushing in/pulling out the plunger.
• Change in temperature : If the temperature of an equilibrium mixture is increased, the rates of both the forwards and backwards reactions will increase. However, the increase in rate of the endothermic reaction > the rate of the exothermic reaction, so the position of equilibrium will shift the favour the endothermic reaction.
• Change in temperature : Decreasing temperature favours the exothermic reaction (-ve enthalpy change) as heat needs to be gained, so the yield of exothermic products will increase.
• Endothermic reactions have a positive (+ve) enthalpy change (*triangle* H). Exothermic reactions have negative (-ve) enthalpy change (*triangle* H).
• Effects of a catalyst : the rate of the forwards and backwards reaction will increase, however the increase in rate will be the same for both. Therefore, the equilibrium position will not shift.
• Effects of a catalyst : They allow equilibrium to be achieved faster, rather than changing the position of equilibrium.