equilibrium

• Chemical equilibrium


  All reversible reactions reach a dynamic equilibrium state
• Dynamic equilibrium


  1. Forward and backward reactions are occurring at equal rates

  2. Concentrations of reactants and products stays constant

  3. Reaction is continuous
• Position of equilibrium


  Describes the composition of the equilibrium mixture
• Position of equilibrium favouring reactants

  Equilibrium mixture will contain mostly reactants
• Le Chatelier's principle


  If an external condition is changed the equilibrium will shift to oppose the change (and try to reverse it)
• If temperature is increased

  Equilibrium will shift in the endothermic direction to try to reduce the temperature
• If temperature is decreased


  Equilibrium will shift in the exothermic direction to try to increase the temperature
• Low temperatures may give a higher yield of product but will also result in slow rates of reaction
• If pressure is increased


  Equilibrium will shift towards the side with fewer moles of gas to try to reduce the pressure
• If pressure is decreased


  Equilibrium will shift towards the side with more moles of gas to try to increase the pressure
• If the number of moles of gas is the same on both sides of the equation then changing pressure will have no effect on the position of equilibrium
• Increasing the concentration of OH- ions

  Equilibrium shifts in the forward direction to remove OH- ions
• Adding H+ ions


  Equilibrium shifts back to the left
• A catalyst has no effect on the position of equilibrium, but it will speed up the rate at which the equilibrium is achieved
• Industrial processes using equilibrium

  • Haber process
  • Contact process
  • Hydration of ethene
  • Production of methanol from CO
• Recycling unreacted reactants back into the reactor can improve the overall yields of these processes
• High pressure leads to too high energy costs for pumps and too high equipment costs
• Catalysts speed up the rate, allowing lower temperatures to be used but have no effect on equilibrium