Chemical equilibrium & le chat

• Le Chatelier's principle only deals with reversible reactions
• reversible reactions - a reaction that can and does go in both directions until an equilibrium is reached
• rate of reaction is the change in concentration per unit time
• rate is affected by

  temperature

  concentration

  catalyst

  surface area

  nature of reactant
• chemical equilibrium - state when the forward reaction = the reverse reaction
• dynamic equilibrium only occurs in closed reactions
• Le Chatelier's Principle - reactions at equilibrium oppose applied stress
• if we increase reactant - equilibrium moves to the right

  if we decrease reactant - equilibrium moves to the left
• if we decrease product - equilibrium moves to the right

  if we increase product - equilibrium moves to the left
• if we increase temperature - equilibrium moves in the endothermic direction

  if we decrease temperature equilibrium moves in the exothermic direction
• if we increase pressure - equilibrium moves to the side with fewer moles

  if we decrease pressure - equilibrium moves to the side with more moles
• if we increase catalyst - no change, equilibrium gets faster

  if we decrease catalyst - no change, equilibrium gets faster
• Haber's process (N2+3H2⇌2NH3)

  Pressure = 200atm

  temp = 500C

  catalyst = iron

  increasing pressure shifts equil. to the right = ATLCP to decrease pressure (fewer molecules)

  temp= moves it to the left side (temp is a compromise)

  catalyst = doesn't change equil. just makes it faster
• contact processes (SO+02⇌SO3)

  pressure = 1 atm

  temp = 450C

  catalyst = V2O5 (Vanadium(V) oxide)

  pressure = high pressure favours the forward reaction (fewer molecules) however yield satisfactory is at 1atm
• dynamic equilibrium = reaction appears to have stopped but it is continuing in both directions