Equilibrium

• Factors that can alter the position of equilibrium

  • Concentration of reactants or products
  • Pressure
  • Temperature
• Le Chatelier’s principle


  If a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to reduce the disturbance
• Increasing the temperature

  The equilibrium position shifts to the right. (This is because the forward reaction is endothermic. Yield of hydrogen increases)
• Dynamic equilibrium

  It occurs when the rate of forward reaction equals the rate of reverse reaction and the concentration of reactants and products remain constant in a closed system
• Increasing the pressure

  The equilibrium position shifts to the left. This is because the forward reaction produces more moles of gas than the reverse reaction (4 moles of product, 2 moles of reactant). Therefore, the yield of hydrogen decreases
• Using high pressure in the production of hydrogen

  Increases the collision frequency, thus increasing the rate of reaction. It is a compromise pressure between an economically viable rate of reaction and a slightly lower yield of hydrogen
• What effect would increasing the temperature have on the position of equilibrium?
• Explain the Le Chatelier’s principle
• What does dynamic equilibrium mean?
• Suggest and explain why an industrial chemist may use a high pressure for the production of hydrogen from: CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) ΔH°= +210 kJ mol-1
• Changing what factors can alter the position of equilibrium?
• What effect does a catalyst have on the position of equilibrium?
• What effect would increasing the pressure have on the position of equilibrium?
• Kc is relevant for homogeneous systems in equilibrium
• Effect of decreasing temperature in an endothermic reaction on Kc

  Kc decreases
• Effect of a catalyst on the position of equilibrium


  No effect (because catalyst affects rate of forward and reverse reactions equally)
• Units for the value of Kc are mol-1 dm-3
• Implication of Kc being greater or less than 1 for the position of equilibrium

  • Greater than 1 = over to the right
  • Less than 1 = over to the left
• Conditions affecting the value of Kc

  • Concentration
  • Catalyst
  • Pressure
  • Temperature
• Deduction of an expression for Kc

  2[A] + 3[B] + [C] ⇌ [D]+ 4[E]
• Effect of decreasing temperature in an exothermic reaction on Kc

  Kc increases
• Effect of increasing temperature in an endothermic reaction on Kc

  Kc increases
• Effect of increasing temperature in an exothermic reaction on Kc

  Kc decreases