Le Chatelier's Principle

• Le Chatelier's Principle


  Whenever you impose a change on a system at equilibrium, the system will move in such a way as to undo that change or relieve some of that stress
• Le Chatelier's Principle


  1. System is at equilibrium

  2. Impose change on system

  3. System moves to undo change
• Increase reactant concentration

  Reaction shifts to the right
• Decrease reactant concentration

  Reaction shifts to the left
• Increase product concentration

  Reaction shifts to the left
• Decrease product concentration

  Reaction shifts to the right
• Increasing or decreasing any reactant or product in the solid or liquid phase will have no effect on the position of equilibrium
• Equilibrium in a chemical reaction

  1. Forward reaction rate equals reverse reaction rate

  2. Concentrations of products and reactants remain constant
• Equilibrium Constant (K)


  • Equals concentration of products divided by concentration of reactants
  • Does not depend on concentration of solids or liquids, only gases or substances in aqueous solution
• Adding a catalyst speeds up the forward and reverse reactions, but does not affect the position of equilibrium
• Decrease reactant concentration


  Reaction shifts to the left to increase reactant
• Increase product concentration

  Reaction shifts to the left to decrease product
• When the volume of the container is increased, the total pressure decreases
• As the volume of the container is increased

  The total pressure decreases
• As the volume of the container is decreased

  The total pressure increases
• When the total pressure increases

  The system tries to decrease the total pressure
• To decrease the total pressure

  The reaction shifts towards the side with fewer moles of gas (right)
• When the total pressure decreases

  The system tries to increase the total pressure
• To increase the total pressure

  The reaction shifts towards the side with more moles of gas (left)
• As the partial pressure of a reactant increases

  The system shifts away from that reactant to decrease its partial pressure
• Haber Process

  • Pressure is increased
  • Temperature is decreased
  • catalyst is added to produce faster
• Pressure - No. of moles
• If pressure is increased --> least no. of moles --> volume is decreased
• If pressure is decreased --> most no. of moles --> volume is increased
• Exothermic if ΔH= (-) P <--
• Endothermic if ΔH=(+) R -->