Equilibria and Kc

• Le Chateliers Principle

  If a change is made to a closed system at equlibrium, the equilibrium will shift to oppose that change.
• Changing concentrations

  A+B⇌C+D

  e.g. adding extra A. This will cause the equilbrium to shift to oppose that change, and so will shift to the products side to try and reduce the concentration of A. This will result in more C and D being formed.
• Changing pressure

  N₂O₄⇌2NO₂

  • pressure only affects reactions that involve gases
  • if the pressure is increased, the equilibrium will shift to oppose that change and decrease the pressure.
  • this means that it will shift to the left (where there are less moles) because fewer moles exert less pressure
• Changing temperature

  • if the temperature is increased, the equilbrium will shift in the endothermic direction to try and decrease it
  • this depends on the reaction given.
• Catalysts

  Have no effect on position of equilbrium.

  • speeds up rate of reaction by providing an alternative pathway with a lower activation energy for the reaction to occur.
  • allows the reactions in industry to reach equilibrium faster.
• Haber Process

  N2+3H2 ⇌ 2NH3

  • an exothermic reaction
  • raw materials include methane and water to produce CO and hydrogen
  • fed into a converter and an iron catalyst is used to speed up rate of reaction
  • "compromise" reached for position of equilibrium and rate of the reaction- if a high temperature is used the equilibrium will shift to the endothermic side (reactants side) and will decrease it- so a low temp used as an alternative
  • pressure - fewer moles on right hand side and so a high pressure can be used.
• Changing conditions and Kc

  • catalysts have no effect on Kc
  • pressure does not affect Kc
  • temperature affects Kc
  • increasing the temperature of an exothermic reaction will decrease Kc and vice versa
  • increasing the temperature of an endothermic reaction will increase Kc and vice versa