1. Le Chatelier’s Principle Chem 12 Chapter 13, Pg 526-532

2. LeChatelier’s Principle When a system at equilibrium is placed under stress, the system will undergo a change in such a way as to relieve that stress.When a system at equilibrium is placed under stress, the system will undergo a change in such a way as to relieve that stress.

3. Le Chatelier Translated: When you take something away from a system at equilibrium, the system shifts in such a way as to replace what you’ve taken away.When you take something away from a system at equilibrium, the system shifts in such a way as to replace what you’ve taken away. When you add something to a system at equilibrium, the system shifts in such a way as to use up what you’ve added.When you add something to a system at equilibrium, the system shifts in such a way as to use up what you’ve added.

4. Le Chatelier Example #1 A closed container of ice and water at equilibrium. The temperature is raised. Ice + Energy  Water The equilibrium of the system shifts to the _______ to use up the added energy. right

5. Le Chatelier Example #2 A closed container of N 2 O 4 and NO 2 at equilibrium. NO 2 is added to the container. N 2 O 4 (g) + Energy  2 NO 2 (g) The equilibrium of the system shifts to the _______ to use up the added NO 2. left

6. Le Chatelier Example #3 A closed container of water and its vapor at equilibrium. Vapor is removed from the system. water + Energy  vapor The equilibrium of the system shifts to the _______ to replace the vapor. right

7. Le Chatelier Example #4 A closed container of N 2 O 4 and NO 2 at equilibrium. The pressure is increased. N 2 O 4 (g) + Energy  2 NO 2 (g) The equilibrium of the system shifts to the _______ to lower the pressure, because there are fewer moles of gas on that side of the equation. left

8. Pressure Changes to system If the volume decreases, the concentration increases, and there will be a shift to the side with the less amount of moles. If the volume increases, the concentration decreases, and there will be a shift to the side with the more amount of moles.

9. Example; If I increase the pressure, where is the shift? (right) If I decrease the pressure, where is the shift? (left) 2SO 2 + O 2 2SO 3 (3moles)(2moles)

10. Effect of Concentration 1.If you add more reactant, it shifts to the right increasing the formation of product, using up the reactants. 2.If you add product, it shifts to the left 3.If you remove product, it shifts to the right, increasing the formation of product. 4.If you remove reactant, it shifts to the left

11. Effect of temperature Energy is treated as a reactant if endothermic equation, and as a product if exothermic equation. If cooling a system, then it shifts so more heat is produced. If heating a system, the shifts so extra heat is used up.

12. Example for temp. changes for Endothermic Reaction Heating the below reaction causes the system to shift to the right = more products, because you treat energy like a reactant. 2NaCl +H 2 SO 4 + energy 2HCl + Na 2 SO 4 Cooling the above reaction causes the system to shift to the left = less reactants, so need to make up more

13. Effect of temp change on exothermic reactions Heating the below reaction causes the system to shift to the left, to use up the extra heat. 2SO 2 + O 2 2SO 3 + energy Cooling the above reaction causes the system to shift to the right, to make up for the lost heat.

14. Homework: Page 529 #33-37