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Le Châtelier’s Principle

Le Châtelier’s Principle. What is it?. When a chemical system at equilibrium is disturbed, the system shifts in a direction that minimizes the disturbance (the system will respond to relieve the stress and re-establish equilibrium). Changes in Concentration.

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Le Châtelier’s Principle

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  1. Le Châtelier’s Principle

  2. What is it? When a chemical system at equilibrium is disturbed, the system shifts in a direction that minimizes the disturbance (the system will respond to relieve the stress and re-establish equilibrium).

  3. Changes in Concentration • An increase in the concentration of a species will shift the equilibrium to the opposite side. • A decrease in concentration of a species will shift the equilibrium to the same side.

  4. Changes in Concentration

  5. Changes in Pressure (Only affects gases) • An increase in pressure will shift the equilibrium to the side with fewer gaseous molecules. Nature can reverse the pressure increase by decreasing the number of collisions. • A decrease in pressure will shift the equilibrium to the side with more gaseous molecules. Nature can reverse the pressure reduction by increasing the number of collisions.

  6. Pressure Practice Problems 4 2 3 2 1 1

  7. Changes in Volume For Gas Systems • Volume changes are interpreted as pressure changes from Boyle’s Law. Decreasing the volume will increase the pressure and increasing the volume will decrease the pressure. • Increasing the volume causes the reaction to shift in the direction that has more moles of gas particles • Decreasing the volume causes the reaction to shift in the direction that has fewer moles of gas particles

  8. Volume Practice Problems 2 4 3 2

  9. Changes in Volume For Saturated Solutions

  10. Changes in Temperature

  11. Temperature Practice Problems Endo Exo Exo Endo Exo Endo Endo Exo

  12. Common Ion Effect Adding similar ions will shift equilibrium Addition of a substance containing an ion that is common to the equilibrium system will increase the concentration of that ion, and the equilibrium will shift to reduce the concentration of that ion

  13. Common Ion Practice Problems

  14. Adding a Catalyst • Catalyst – a substance that increases the rate of a chemical reaction but is not consumed by the reaction • Catalysts lower the activation energy making it easier for reactants to get over the energy hump. • Activation energy – amount of energy that must be absorbed by reactants before a reaction can occur; an energy hump that normally exists between the reactants and products. • Activated Complex – point at which the reaction will go to completion or go back to reactants. • Enthalpy (ΔH) is the energy difference between the reactants and products • Exothermic reactions have a negative ΔH • Endothermic reactions have a positive ΔH

  15. Adding a Catalyst • A catalyst does not change the position of equilibrium; only how fast equilibrium is reached. • A catalyst does not change the value of Keq for a reaction; it affects only the rate of reaction

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