topic 10 equilibrium

• why are catalyst used in industrial processes?

  • catalyst increases the rate at which the reaction moves towards equilibrium.
  • decreases the time a reaction takes to arrive at a particular yield of a product.
  • provides an alternate reaction pathway, promoting a lower activation energy.
  • & allows milder conditions to be used, therefore lowering the cost.
• effect of increased temp. on equilibrium

  • if temp is increased,
  • equilibrium will shift to oppose this,
  • & move in the endothermic, backwards reaction,
  • to try & decrease the temp by absorbing heat energy.
  • the position of equilibrium will shift towards the left,
  • giving a lower yield of the substance.
• effect of decreased temp on equilibrium:

  • if temp is decreased,
  • equilibrium will shift to oppose this,
  • & move in the exothermic, forward direction,
  • to try & increase the temp by giving out heat energy.
  • the position of equilibrium will shift towards the right,
  • giving higher yield of the substance.
• effect of increased pressure on equilibrium:

  • if pressure is increased,
  • equilibrium will shift to oppose this,
  • & move towards the side with fewer moles of gas to try to reduce the pressure.
  • the position of equilibrium will shift towards the *right/left
  • (describe the moles on both sides shown)
  • giving higher yield of a substance
• Kc formula


  Kc = [C]p [D]q / [A]m [B]n

  A, B, C, D = chemical formula

  m, n, p, q = stoichiometric balance number (moles)
• effect of decreased pressure on equilibrium:

  • if the pressure is decreased,
  • the equilibrium will shift to oppose this,
  • & move towards the side with more moles,
  • to try & increase the pressure,
  • the position of equilibrium will shift towards the fewer moles because there are,
  • (describe the moles shown)
  • giving lower yield of a substance.
• • in all cases, high pressure leads to too high energy costs,
  • for pumps to produce pressure,
  • & too high equipment costs to have certain apparatus,
  • that can withstand high pressures
• larger the Kc

  greater amount of products
• smaller Kc

  the equilibrium favours the reactants
• what one thing is Kc only affected by

  temp
• Haber Process: N2 (g) + 3H2 (g) ⇌ 2NH3 (g)

  • The reaction is exothermic in the forward direction
  • Therefore, an increase in temperature may increase the rate of reaction but it will decrease the overall yield as the equilibrium shifts to the left.
  • An increase in pressure will increase the yield
  • This is because there are 4 moles of reactant compared to only 2 moles of product.
• The value of Kc indicates the position of equilibrium:

  Kc = 1 - the position of equilibrium is halfway between the reactants and products.

  Kc < 1 - the position of equilibrium lies towards the left-hand side, i.e. the reactants.

  Kc > 1 - the position of equilibrium lies towards the right-hand side, i.e. the products.
• Effect of an increase in pressure on the rate of reaction:

  • Rate increases because there are more molecules per unit volume; [1 mark]
  • So there is an increase in the frequency of collisions between reacting molecules; [1 mark]
• Heterogeneous means:

  • The catalyst is in a different phase of state to the reactants

  A catalyst has no effect on the yield of the products in the reaction because:

  • A catalyst increases the rate of the forward and backward reactions