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• Generalised reaction


  mA + nB ⇌ pC + qD
• Stoichiometric balancing numbers


  m, n, p, q
• Equilibrium constant


  Kc = [C]^p [D]^q / [A]^m [B]^n
• Equilibrium constant expression


  Kc = [NH3 (g)]^2 / ([N2 (g)] [H2 (g)]^3)
• Unit of Kc


  • Depends on the balanced equation
  • Can be calculated by putting the unit of concentration (mol dm-3) into the Kc expression
• Calculating Kc


  1. Work out equilibrium moles

  2. Calculate equilibrium concentrations

  3. Put concentrations into Kc expression
• Practical: Determining Kc


  1. Prepare equilibrium mixture

  2. Titrate equilibrium mixture

  3. Calculate equilibrium amounts

  4. Calculate Kc
• Partial pressure of a gas in a mixture is the pressure the gas would have if it alone occupied the volume of the whole mixture
• Calculating equilibrium amounts


  1. Calculate the equilibrium amount of ethanol, ethyl ethanoate and water

  2. Amount of ethanoic acid that reacted = initial amount – equilibrium amount

  3. Amount of ethanol at equilibrium = initial amount - amount that reacted

  4. Amount of ethyl ethanoate at equilibrium = initial amount + amount that formed

  5. Amount of water at equilibrium = initial amount + amount that formed
• Partial pressure


  The pressure that the gas would have if it alone occupied the volume occupied by the whole mixture
• Kp


  Equilibrium constant based on partial pressures
• Kp expressions only contain gaseous substances. Any substance with another state is left out.
• Heterogeneous equilibria for Kp


  Kp = p(CO2)
• Changing concentration would shift the position of equilibrium but the value of Kc would not change.
• Kc and Kp only change with temperature. They do not change if pressure or concentration is altered.
• A catalyst also has no effect on Kc or Kp
• If temperature is increased

  The reaction will shift to oppose the change and move in the backwards endothermic direction. The position of equilibrium shifts left. The value of Kc gets smaller as there are fewer products.
• Catalysts have no effect on the value of Kc or Kp or the position of equilibrium as they speed up both forward and backward rates by the same amount.
• If pressure is increased

  The reaction will shift to oppose the change and move in the forward direction to the side with fewer moles of gas. The position of equilibrium shifts right. The value of Kc stays the same though as only temperature changes the value of Kc.