1. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Electrochemistry The study of the interchange of chemical and electrical energy.

2. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Review of Terms oxidation-reduction (redox) reaction: involves a transfer of electrons from the reducing agent to the oxidizing agent. oxidation: loss of electrons reduction: gain of electrons

3. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 Half-Reactions The overall reaction is split into two half-reactions, one involving oxidation and one reduction. 8H + + MnO 4  + 5Fe 2+  Mn 2+ + 5Fe 3+ + 4H 2 O Reduction: 8H + + MnO 4  + 5e   Mn 2+ + 4H 2 O Oxidation: 5Fe 2+  5Fe 3+ + 5e 

4. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Figure 17.1 Schematic of a Method to Separate the Oxidizing and Reducing Agents of a Redox Reaction

5. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Voltaic Cell A device in which chemical energy is changed to electrical energy.

6. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 Figure 17.2 Voltaic Cells

7. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 Anode and Cathode OXIDATION occurs at the ANODE. REDUCTION occurs at the CATHODE.

8. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 Figure 17.3 An Electrochemical Process Involves Electron Transfer at the Interface Between the Electrode and the Solution

9. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 Figure 17.4 Digital Voltmeters

10. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Figure 17.5 A Zn/H Galvanic Cell

11. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Figure 17.6 A Zn/Cu Voltaic Cell

12. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Figure 17.7 A Schematic of a Galvanic Cell

13. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Figure 17.8 A Schematic of a Galvanic Cell

14. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Cell Potential Cell Potential or Electromotive Force (emf): The “pull” or driving force on the electrons.

15. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Standard Reduction Potentials The E  values corresponding to reduction half-reactions with all solutes at 1M and all gases at 1 atm. Cu 2+ + 2e   Cu E  = 0.34 V vs. SHE SO 4 2  + 4H + + 2e   H 2 SO 3 + H 2 O E  = 0.20 V vs. SHE

16. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 emf and Work

17. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 Batteries A battery is a voltaic cell or, more commonly, a group of voltaic cells connected in series.

18. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 Figure 17.14 A Common Dry Cell Battery

19. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 Fuel Cells...voltaic cells for which the reactants are continuously supplied. 2H 2 (g) + O 2 (g)  2H 2 O(l) anode: 2H 2 + 4OH   4H 2 O + 4e  cathode: 4e  + O 2 + 2H 2 O  4OH 

20. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20 Figure 17.16 Schematic of the Hydrogen-Oxygen Fuel Cell

21. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 Electrolysis...forcing a current through a cell to produce a chemical change for which the cell potential is negative.

22. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 Stoichiometry of Electrolysis 4 How much chemical change occurs with the flow of a given current for a specified time? current and time  quantity of charge  moles of electrons  moles of analyte  grams of analyte