Entry Task: Jan 14 th Monday

1. Entry Task: Jan 14th Monday If we have a Q value of 2.3 and a K value of 2.3 x 10-3 which way should the equilibrium shift? You have 5 minutes!

2. Agenda: • Sign off discuss Ch. 15. sec. 5-6 reading notes • HW: LeChatelier ws

4. WARNING!!Black text slides are embedded notes

5. The Reaction Quotient (Q) • To calculate Q, substitute the initial concentrations on reactants and products into the equilibrium expression. • Q gives the same ratio the equilibrium expression, but for a system that is not at equilibrium.

6. If Q = K, the system is at equilibrium.

7. If Q > K, there is too much product and the equilibrium shifts to the left.

8. If Q < K, there is too much reactant, and the equilibrium shifts to the right.

9. First provide which way the equilibrium constant will favor in the reaction then provide the direction of Q will favor. Reactants Reactants K= 2.6 x 10-4__________ Verses Q = 1.2 x 10-2___________ K= 3.5 x 101__________ Verses Q = 6.8 x 10-2____________ K= 9.8 x 10-1__________ Verses Q = 9.8 x 10-1____________ Product Product Equal Equal

10. 1. The equilibrium constant is 0.0900 at 25ºC for the reaction H2O(g) + Cl2O(g) ↔ 2 HOCl(g) For which of the following sets of conditions is the system at equilibrium? For those which are not at equilibrium, in which direction will the system shift? (a) PH2O= 200. torr, PCl2O= 49.8 torr, PHOCl= 21.0 torr (b) PH2O= 296 torr, PCl2O= 15.0 torr, PHOCl= 20.0 torr (c) A 2.0-L flask contains 0.084 mol HOCl, 0.080 Cl2O, and 0.98 mol H2O. (d) A 3.0-L flask contains 0.25 mol HOCl, 0.0010 mol Cl2O, and 0.56 mol H2O

11. 1. The equilibrium constant is 0.0900 at 25ºC for the reaction H2O(g) + Cl2O(g) ↔ 2 HOCl(g) For which of the following sets of conditions is the system at equilibrium? For those which are not at equilibrium, in which direction will the system shift? (a) PH2O= 200. torr, PCl2O= 49.8 torr, PHOCl= 21.0 torr H2O(g) + Cl2O(g) → 2 HOCl(g)

12. 1. The equilibrium constant is 0.0900 at 25ºC for the reaction H2O(g) + Cl2O(g) ↔ 2 HOCl(g) For which of the following sets of conditions is the system at equilibrium? For those which are not at equilibrium, in which direction will the system shift? (b) PH2O= 296 torr, PCl2O= 15.0 torr, PHOCl= 20.0 torr = 0.0901  K; its at equilibrium

13. 1. The equilibrium constant is 0.0900 at 25ºC for the reaction H2O(g) + Cl2O(g) ↔ 2 HOCl(g) For which of the following sets of conditions is the system at equilibrium? For those which are not at equilibrium, in which direction will the system shift? (c) A 2.0-L flask contains 0.084 mol HOCl, 0.080 Cl2O, and 0.98 mol H2O. Change to molarity 0.084/2.0 = 0.042 M HOCl 0.080/2.0 = 0.040 M Cl2O 0.98/2.0 = 0.45 M H2O = 0.098  K; its at equilibrium

14. 1. The equilibrium constant is 0.0900 at 25ºC for the reaction H2O(g) + Cl2O(g) ↔ 2 HOCl(g) For which of the following sets of conditions is the system at equilibrium? For those which are not at equilibrium, in which direction will the system shift? (d) A 3.0-L flask contains 0.25 mol HOCl, 0.0010 mol Cl2O, and 0.56 mol H2O Change to molarity 0.25/3.0 = 0.083 M HOCl 0.0010/3.0 = 3x10-4 M Cl2O 0.56/3.0 = 0.186 M H2O = 123 > K; reaction will proceed to the left (reactants)

15. Le Châtelier’s Principle “If a system at equilibrium is disturbed by a change in temperature, pressure, or the concentration of one of the components, the system will shift its equilibrium position so as to counteract the effect of the disturbance.”

16. Le Châtelier’s Principle • System starts at equilibrium. • A change/stress is then made to system at equilibrium. • Change in concentration • Change in volume • Change in pressure • Change in Temperature • Add Catalyst • System responds by shifting to reactant or product side to restore equilibrium.

17. Remove Remove Add Add aA + bBcC + dD Le Châtelier’s Principle • Changes in Concentration Change Shifts the Equilibrium Increase concentration of product(s) Left- reactants Decrease concentration of product(s) Right-products Increase concentration of reactant(s) Right- products Decrease concentration of reactant(s) Left- reactants

18. A (g) + B (g) C (g) Le Châtelier’s Principle • Changes in Volume and Pressure • (Only a factor with gases) Change Shifts the Equilibrium Increase pressure Side with fewest moles of gas Decrease pressure Side with most moles of gas Increase volume Side with most moles of gas Decrease volume Side with fewest moles of gas 14.5

19. Le Châtelier’s Principle • When temp is increased, the equilibrium shifts in the direction that absorbs heat Change Exothermic Rx Endothermic Rx Increase temperature K and reactants K and product Decrease temperature K and product K and reactants 14.5

20. Le Châtelier’s Principle • Adding a Catalyst • does not change K • does not shift the position of an equilibrium system • system will reach equilibrium sooner

21. uncatalyzed catalyzed Catalyst lowers Ea for both forward and reverse reactions. Catalyst does not change equilibrium constant or shift equilibrium. 14.5

22. No change No change Decrease amt No change Decrease amt   Increase amt No Change 