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Chapter 18

Chapter 18. Redox and Electrochemistry Suroviec Spring 2014. I. Electron Transfer Reaction. Study of interconversion of electrical and chemical energy. 2 types of cells. I. Electron transfer reactions. Cu°(s) + 2Ag + (aq)  Cu 2+ (aq) + 2Ag ° (s). A. Balancing in Acidic solution.

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Chapter 18

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  1. Chapter 18 Redox and Electrochemistry Suroviec Spring 2014

  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)  Cu2+(aq) + 2Ag°(s)

  4. A. Balancing in Acidic solution • Balance the following in acid: Al(s) + Cu2+(aq)  Al3+(aq) + Cu(s)

  5. B. Balancing in Base • Balance the following in base I-(aq) + MnO4-(aq)  I2(aq) + MnO2(s)

  6. II. Voltaic Cells Lets take: Cu°(s) + 2Ag+(aq)  Cu2+(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

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

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

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

  13. IV. E° , DG° and Keq • E° , DG° It can be shown that DG° = -nFE°

  14. B. E° and Keq • Redox equations also have a state of equilibrium which means that DG° = -RT lnKeq

  15. Example • For this reaction, determine DG° and Keq at 25°C 3Fe2+(aq) + NO3-(aq) +4H+(aq)  NO(g) + 2H2O(l) + 3Fe3+(aq)

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

  17. Example • Given this reaction where all the concentrations are 2.5x10-2 M, calculate Q, n, E0 and E Zno(s) + 2H2O(l) + 2OH-(aq)  [Zn(OH)4]2-(aq) + H2(g)

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

  19. Example • Chromium can be electroplated onto other surfaces: Cr2O72- (aq) + 14H+ (aq) + 12e-2Cr (s) + 7H2O (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?

  20. Example • A baby spoon with an area of 6.25cm2 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)

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