1. Section 8.4—Le Chatelier’s Principle How can we push a reaction to make more products?

2. Le Chatelier’s Principle – If a system at equilibrium is disturbed, it will shift to re-establish equilibrium A system will try to un-do whatever you’ve done Le Chatelier’s Principle

3. Increasing Concentrations Adding a reactant Q becomes too small There’s too many reactants Reaction shifts to right (get rid of extra reactants and make more products) Adding a product Q becomes too large There’s too many products Reaction shifts to left (get rid of extra products and make more reactants)

4. Removing a reactant Q becomes too large There’s too few reactants Reaction shifts to left (make more reactants) Removing a product Q becomes too small There’s too few products Reaction shifts to right (make more products) Decreasing Concentrations

5. Decrease volume Pressure increases Reaction shifts to the side with least moles of gas to decrease pressure Increase volume Pressure decreases Reactions shifts to the side with the most moles of gas to increase pressure Changes in Pressure

6. Endo & Exothermic Endothermic Reaction – The reaction takes in energy…the products have more energy than the reactants Exothermic Reaction – The reaction gives off energy…the products have less energy than the reactants Energy is a reactant in the reaction Energy is a product in the reaction

7. Increase temperature of endothermic reaction Increasing a reactant Decrease temperature of endothermic reaction Remove a reactant Reaction shifts to right (get rid of extra reactants and make more products) Reaction shifts to left (make more reactants) Changing temperature—Endothermic

8. Increase temperature of exothermic reaction Increasing a product Decrease temperature of exothermic reaction Remove a product Reaction shifts to left (get rid of extra products and make more reactants) Reaction shifts to right (make more products) Changing Temperature—Exothermic

9. Adding a pure solid or liquid reactant or product  They’re not in the equilibrium constant expression Increasing pressure by adding an inert gas  They’re not in the equilibrium constant expression Changing the volume of a reaction with an equal number of moles of gas on each side of the reaction  The system won’t gain anything by shifting since both sides will cause the same pressure Adding a catalyst  A catalyst will speed up how fast equilibrium is established— but not the number of reactants and products once it’s at equilibrium Some changes have no effect!

10. NH 4 Cl (s)  NH 3 (g) + HCl (g) Removing some NH 4 Cl Adding HCl Adding Ne (g) Decreasing volume Examples Example: Which way will the reaction shift for each of the following changes:

11. NH 4 Cl (s)  NH 3 (g) + HCl (g) Removing some NH 4 Cl Adding HCl Adding Ne (g) Decreasing volume No change (it’s an inert gas) No change (it’s a solid) (Adding a product) (Goes to side with least gas moles) Examples Example: Which way will the reaction shift for each of the following changes:

12. 2 SO 2 (g) + O 2 (g)  2 SO 3 (g) an exothermic reaction Increasing volume Raising temperature Adding O 2 Removing SO 2 Let’s Practice Which way will the reaction shift for each of the following changes:

13. 2 SO 2 (g) + O 2 (g)  2 SO 3 (g) an exothermic reaction Increasing volume Raising temperature Adding O 2 Removing SO 2 (Goes to side with most gas moles) (Energy is a product) (Adding a reactant) (Removing a reactant) Let’s Practice Which way will the reaction shift for each of the following changes: