1. REDOX AND ELECTROCHEMISTRY SUROVIEC SPRING 2015 Chapter 18

2. I. Electron Transfer Reaction Study of interconversion of electrical and chemical energy 2 types of cells

3. I. Electron transfer reactions Cu°(s) + 2Ag + (aq)  Cu 2+ (aq) + 2Ag ° (s)

4. A. Balancing in Acidic solution Balance the following in acid: Al(s) + Cu 2+ (aq)  Al 3+ (aq) + Cu(s)

5. B. Balancing in Base Balance the following in base I - (aq) + MnO 4 - (aq)  I 2 (aq) + MnO 2 (s)

6. II. Voltaic Cells Lets take: Cu°(s) + 2Ag + (aq)  Cu 2+ (aq) + 2Ag ° (s) and make a voltaic cell around it

7. B. Other Salt Bridge Cells

8. III. Standard Voltages The driving force behind a spontaneous reaction in a voltaic cell is measure by cell voltage.

9. A. E° RED + E° ox Any redox reaction can be split into 2 ½ reactions each with its own E° and therefore its own

11. A. E° cathode and E° anode Notice on the table only E° RED is listed

12. B. Strength of oxidizing and reducing agents Oxidizing agents = species that can electrons Reducing agents = species that supply electrons

13. C. Calculations of E° and spontaneity To determine if a reaction is spontaneous look at the sign of E°

14. IV. E°,  G° and K eq A. E°,  G° It can be shown that  G° = -nFE°

15. B. E° and K eq Redox equations also have a state of equilibrium which means that  G° = -RT lnK eq

16. Example For this reaction, determine  G° and K eq at 25°C 3Fe 2+ (aq) + NO 3 - (aq) +4H + (aq)  NO(g) + 2H 2 O(l) + 3Fe 3+ (aq)

17. V. Concentration and Voltage What if we are not at standard state? When the concentrations change the voltage must also change

18. Example Given this reaction where all the concentrations are 2.5 x 10 -2 M, calculate Q, n, E 0 and E Zn o (s) + 2H 2 O(l) + 2OH - (aq)  [Zn(OH) 4 ] 2- (aq) + H 2 (g)

19. VI. Electrolytic Cells Non-spontaneous reactions made to occur by pushing electrical energy through the system

20. Example Chromium can be electroplated onto other surfaces: Cr 2 O 7 2- (aq) + 14H + (aq) + 12e -  2Cr (s) + 7H 2 O (l) Using a current of 8.00A and 3.5V, how many grams of chromium can be plated is the experiment is run for a hour?

21. Example A baby spoon with an area of 6.25cm 2 is plated with silver from AgCl (s) using 2.00A for 2 and ¼ hours. If the current efficiency is 82% how many grams of Ag is plated? AgCl (s) + e -  Ag (s) + Cl - (aq)