Chem - Equilibria

• Dynamic Equilibrium

  Dynamic equilibrium state where forward and backward reactions are occurring at equal rates, resulting in constant concentrations of reactants and products
• Reaching equilibrium

  Reversible reactions reach an equilibrium state
• Position of equilibrium

  Describes the composition of the equilibrium mixture
• Reactant-favoured equilibrium


  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
• Increasing temperature

  Equilibrium shifts in the endothermic direction to absorb heat and reduce temperature
• Decreasing temperature


  Equilibrium shifts in the exothermic direction to give out heat and increase temperature
• Increasing pressure

  Equilibrium shifts towards the side with fewer moles of gas to reduce pressure
• Decreasing pressure

  Equilibrium shifts towards the side with more moles of gas to increase pressure
• A catalyst has no effect on the position of equilibrium, but it will speed up the rate at which the equilibrium is achieved
• Haber process


  • T= 450oC, P= 200 – 1000 atm, catalyst = iron
  • Compromise temperature used to balance yield and rate
  • High pressure gives good yield and rate but high energy costs
• 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 temp to be used but have no effect on equilibrium
• Kc


  Equilibrium constant, the larger the Kc the greater the amount of products. If Kc is small the equilibrium favours the reactants.
• Kc only changes with temperature, not pressure or concentration. A catalyst also has no effect on Kc.
• Liquid and solid concentrations are constant, and are not included in heterogeneous Kc expressions.
• If more product is added to a reaction, the concentration of product increases, causing the system to shift back towards the reactant side until equilibrium is re-established.
• If we increase pressure on a reaction with gases, it shifts towards the side with fewer moles of gas (to decrease pressure)
• Le Chatelier's principle states that if an external factor changes, then the position of equilibrium will change so as to counteract the effect of the change.
• Le Chatelier's principle states that if an external factor changes, the system will shift so as to counteract this change
• The equilibrium constant is the ratio of products to reactants at equilibrium.