le chatelier's principle/dynamic equilibrium

• Position of equilibrium


  The relative quantities of reactants and products, indicating the extent of a reversible reaction at equilibrium.
• Reversible reaction

  A reaction that takes place in both 'forward' and 'reverse' directions.
• Closed system

  A system isolated from its surroundings
• Dynamic equilibrium

  The equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction and concentrations do not change
• le chatelier's principle

  when a system in dynamic equilibrium is subjected to external change, the system readjusts itself to minimise the effect of the change and to restore equilibrium
• in a equilibrium system

  • the rate of the forward reaction is equal to the rate of the reverse reaction
  • the concentrations of the reactants and products do not change
• for a reaction to remain in equilibrium, the system must be closed
• the effect of changing concentration on equilibrium

  • if there are more products formed, equilibrium shifts to the right
  • if there are more reactants formed, equilibrium shifts to the left
• the effect of changing temperature on equilibrium

  • an increase in temperature will shift equilibrium to the endothermic direction (ΔH is positive)
  • a decrease in temperature will shift equilibrium to the exothermic direction (ΔH is negative)
• if FORWARD reaction was endothermic (ΔH is positive), an INCREASE in temperature would

  • shift equilibrium to the right
  • more products made
• if FORWARD reaction was endothermic (ΔH is positive), a DECREASE in temperature would

  • shift equilibrium to the left
  • more reactants made
• if FORWARD reaction was exothermic (ΔH is negative), an INCREASE in temperature would

  • shift equilibrium to the left
  • more reactants made
• if FORWARD reaction was exothermic (ΔH is negative), an DECREASE in temperature would

  • shift equilibrium to the right
  • more products made
• the effect of changing pressure on equilibrium

  • an increase in pressure, shifts towards fewer gaseous molecules
  • a decrease in pressure, shifts towards more gaseous molecules
• a catalyst does not change the position of equilibrium but speeds up the rates of the foward and reverse of reactions equally
• At dynamic equilibrium, forward and reverse reactions occur at the same rate. No change in concentration.
• To maximise yield of Haber process:

  • high pressure
  • 1ow temp
• N2 (g) + 3H2 (g) = 2 NH3 (g) △H = - ve
• Exothermic reaction

  System releases heat energy to surroundings, △H negative
• Endothermic reaction

  System takes in heat energy from surroundings, △H positive
• what diagram is this?

  exothermic

  
• what reaction is this?

  endothermic