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 17 Electrochemistry

3. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 Electrochemistry The study of the interchange of chemical and electrical energy. Processes involve Oxidation-Reduction Reactions.

4. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Section 17.3 Cell Potential, Electrical Work, & Free Energy Exploring the relationship between Thermodynamics and Electrochemistry Work that can be accomplished when e - ’s are transferred through a wire depends on the “push” (the thermodynamic driving force) behind the e - ’s.

5. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Driving force = emf (Electromotive Force) Section 17.3 Cell Potential, Electrical Work, & Free Energy (between 2 pts. in circuit)

6. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 When a cell produces current, The cell potential is positive Work will be done by the system (  work is negative) E = - w/q E = -work charge

7. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 Thus, w max = -q E max In any real, spontaneous process, some energy is always wasted. The actual work realized is always less than the calculated maximum. Work is lost as frictional heating when the current passes through a wire.

8. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 From Chapter 16  G = w max = - q E max q = quantity of charge in coulombs transferred Charge on 1 mole of e - ’s is a constant called the faraday (F) = 96485 coulombs of charge per mole of e - ’s

9. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 q = quantity of charge in coulombs transferred q = nF q = (# of mole of e - ’s) x (96485 C/mole of e - )

10. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 From Chapter 16  G = w max = - q E max Since q = n F then  G = - n F E max

11. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Free Energy and Cell Potential  G  =  nFE  n = number of moles of electrons F = Faraday = 96,485 coulombs per mole of electrons “The maximum cell potential is directly related to The free energy difference between the reactants And the products in the cell.”

12. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Free Energy and Cell Potential  G  =  nFE  Equation provides experimental means to obtain  G for a reaction. Confirms that a galvanic cell will run in direction that gives a positive E cell. Positive E cell gives a negative  G.

13. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Section 17.4 Dependence of Cell Potential on Concentration So far, cells are at standard conditions. If we change the concentration, qualitatively we can predict how the cell potential would be affected by using LeChatelier’s Principle..

14. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Concentration Cell...a cell in which both compartments have the same components but at different concentrations.

15. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Figure 17.9 A Concentration Cell That Contains a Silver Electrode and Aqueous Silver Nitrate in Both Compartments Driving force will transfer e - ’s for L  R. Ag deposits on Rt. Ag dissolves on Lt.

16. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 Left side 0.1 M Ag + Right side 1.0 M Ag + Nature will try to equalize the concentration of Ag + in the 2 compartments. Driving force will transfer e - from the L  R. Ag will be deposited on the right electrode. Ag will dissolve on the left to increase conc. of Ag + in the sol’n.

17. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 Recall  G =  G  + RT ln Q -n F E = - n F E  + RT ln Q Rearranged E = E  - RT ln Q nF

18. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 The Nernst Equation We can calculate the potential of a cell in which some or all of the components are not in their standard states. Valid at 25  C.

19. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 Nernst Equation calculates the maximum potential before any current flow has occurred. As the cell discharges & current flows, concentrations will change and therefore, E cell changes.

20. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20 Cell will spontaneously discharge until it reaches equilibrium, i.e., until  G = 0. Then E cell = 0 And Q = K “Dead Battery”: Cell no longer able to do work!

21. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 Calculation of Equilibrium Constants for Redox Reactions At equilibrium, E cell = 0 and Q = K.

22. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 Since cell potential is sensitive to the conc. of reactants & products, measured potentials can be used to determine the conc. of an ion.

23. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23 Figure 17.12 A Glass Electrode for Measuring pH When electrode is dipped in a sol’n., the electrode potential determined by the difference in [H + ] between the 2 sol’ns.  pH.

24. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 24 Other electrodes are sensitive to the Concentrations of other particular ions. Þ Ion-Selective Electrodes. See Table 17.2.

25. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 25 Figure 17.11 Schematic Diagram of the Cell Described in Sample Exercise 17.7 Read Sample Exercise 17.7.