Topic 10 - Equilibrium

• You can tell if a reaction is reversible or not by measuring the concentrations of reactions and products
• Equilibrium is established when the rates of the forwards and backwards reactions are equal
• Two conditions needed for dynamic equilibrium:

  • The reaction must be reversible
  • Must be in a closed system
• Three features of dynamic equilibrium:

  • Both forward and backward reactions are continuously occurring
  • The rate of the forward reaction is equal to the rate of the backward reaction
  • The concentrations of reactants and products remain constant
• Four factors that affect equilibrium:

  • Concentration of a component
  • Pressure of a system
  • Temperature of a system
  • Addition of a catalyst
• If concentration of something is increased, equilibrium will shift to use up more of that substance and return to original concentration
• Changing pressure only applies to reversible reactions of gases
• When pressure is increased, equilibrium will shift to favour the side with less moles
• If temperature is increased, equilibrium will shift towards the endothermic reaction to absorb the energy
• A catalyst does not affect equilibrium position however it will speed up reaction and cause it to reach equilibrium faster
• Sometimes equilibria predictions do not work, for example if an exothermic reaction with less moles on the product side is placed in hot water, both pressure and temperature increase
• All reactions reach a dynamic equilibrium state
• Dynamic equilibrium occurs when backwards and forwards reactions occur at equal rates. The concentrations of products and reactants stays constant.
• The position of equilibrium describes the composition of the mixture
• Le Chaterlier's principle states that if an external condition is applied to the system, the equilibrium will change to oppose the shift
• If the temperature is increases, the rate of the endothermic reaction will increase to absorb the additional energy
• If the temperature is decreased, the rate of the exothermic reaction will increase to release more energy into the system
• Low temperature may give a higher yield of product but will decrease rate of reaction
• Increasing pressure will shift equilibrium towards the side with fewer moles
• If the number of moles is the same on both sides of the equation, increasing the pressure will have no effect
• Increasing the pressure will increase rate of reaction and may produce a higher yield of product but is very expensive
• Catalysts have no effect on position of equilibrium, however the reaction will reach equilibrium faster
• Recycling unreacted reactants into the reactor can improve overall yield
• Taking out product can help to increase yield
• Decreasing the concentration of a product will result in more of it being made
• Kc is equilibrium constant
• Kc is concentration of products to the power of the ratio divided by concentration of reactants to the power of the ratio
• The larger the Kc value, the higher the yield of products
• Kc only changes with temperature
• Solid and liquid concentrations are constant so can be ignored in Kc