1. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Chemistry FIFTH EDITION by Steven S. Zumdahl University of Illinois

2. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Chemistry FIFTH EDITION Chapter 13 Chemical Equilibrium See Schedule for Chapter 13Schedule for Chapter 13

3. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 Section 13.5 Applications of the Equilibrium Constant Allows one to predict (1)Tendency of a rxn. to occur (but not the speed). (2)Whether or not a given set of conc.’s represent an equilibrium condition. (3)The equilibrium position that must be achieved from a given set of initial concentrations.

4. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 The Extent of Reaction Magnitude of the equilibrium constant, K indicates the inherent tendency for a reaction to occur.

5. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 K >> 1 Mostly products at equlibrium. Equilibrium lies to the Right. Reaction goes essentially to completion. K << 1 Mostly reactants at equilibrium. Equilibrium lies to the Left. Reactions does not occur to any significant extent.

6. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 ☻Size of K and Time required to reach equilibrium are Not Related!! K depends on thermodynamic stability. Time to reach equilibrium depends on reaction rate which depends on the size of the activation energy.

7. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 Figure 13.7 The Difference between Thermodynamic and Kinetic Stabilities Magnitude of K depends on  E. Magnitude of rxn. Rate depends on E a.

8. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 Reaction Quotient... helps to determine the direction of the move toward equilibrium. The law of mass action is applied with initial concentrations.

9. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 Reaction Quotient, Q For jA + kB  lC + mD Q = [C]  l [D]  m [A]  j [B]  k Law of Mass Action using initial concentrations.

10. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Reaction Quotient (continued) H 2 (g) + F 2 (g)  2HF(g)

11. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Q = KSystem is at Equilibrium; No shift will.occur. Q > KSystem shifts to the left; Consumes products; Forms more reactant. Q < KSystem shifts to the right; Consumes reactants; Forms more product.

12. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Let’s Do Problems # 33 & 35

13. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Section 13.6 Solving Equilibrium Problems 1.Balance the equation. 2.Write the equilibrium expression. 3.List the initial concentrations. 4.Calculate Q and determine the shift to equilibrium.

14. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Solving Equilibrium Problems (continued) 5.Define equilibrium concentrations. 6.Substitute equilibrium concentrations into equilibrium expression and solve. 7.Check calculated concentrations by calculating K.

15. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Let’s Do Problems # 45 & 46 A bit more complicated! May need the quadratic formula. May use Method of Successive Approximations. (Appendix 1.4) May make simplifications when K is very small. Let’s Do Problems # 47, 49, 51, 53 & 56

16. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 Section 13.7 Le Chatelier’s Principle Used to predict the effects of changes in -- Concentration -- Pressure -- Temperature on a system at Equilibrium.

17. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 Le Châtelier’s Principle... if a change is imposed on a system at equilibrium, the position of the equilibrium will shift in a direction that tends to reduce that change.

18. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 Figure 13.8 A Mixture of N 2, H 2, and NH 3 N 2 + 3 H 2  2NH 3 Calculate K Add N 2, New Equilibrium!! Calculate Q: Q< K Same K Less H 2, More NH 3

19. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 Effects of Changes on the System 1.Concentration: The system will shift away from the added component 2.If a component is removed, the opposite effect will occur. The system will shift toward the removed component.

20. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20 REMEMBER: Pure solids and pure liquids have no effect on the equilibrium position. THEREFORE: Changing their amounts will have no effect.

21. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 Effects of Changes on the System (continued) 2.Pressure: a. Addition of inert gas does not affect the equilibrium position. b. Decreasing the volume shifts the equilibrium toward the side with fewer moles.

22. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 Figure 13.9 The Effect of Decreased Volume on the Ammonia Synthesis Equilibrium N 2 + 3 H 2  2 NH 3

23. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23 Reducing Volume: System shifts toward the side of the rxn. involving the smaller # of gas molecules. Increasing Volume: System shifts toward the side of the rxn. Involving the larger # of gas molecules. When molecules of gas are equal on both sides, equilibrium will not shift if volume changes.

24. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 24 Effects of Changes on the System 3.Changes in Temperature: K will change depending upon the temperature Changes in concentration and pressure causes change in the equilibrium position, but both positions give the same Equilibrium constant, K.

25. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 25 Treat energy as a reactant in an endothermic rxn. Treat energy as a product in an exothermic rxn. System will shift in same way as when an actual reactant or product is added or removed.

26. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 26 For EXOTHERMIC Reaction K  as Temperature  System shifts left. For ENDOTHERMIC Reaction K  as Temperature  System shifts right.

27. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 27 Let’s Do Problems # 59, 61, 63, 64, 71