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  • 1. 20-5 Batteries: Producing Electricity Through Chemical Reactions
    • Primary Cells (or batteries).
      • Cell reaction is not reversible.
    • Secondary Cells.
      • Cell reaction can be reversed by passing electricity through the cell (charging).
    • Flow Batteries and Fuel Cells.
      • Materials pass through the battery which converts chemical energy to electric energy.
    Slide of 54
  • 2. The Leclanch é (Dry) Cell Slide of 54
  • 3. Dry Cell Slide of 54 Zn(s) -> Zn 2+ (aq) + 2 e - Oxidation : 2 MnO 2 (s) + H 2 O(l) + 2 e - -> Mn 2 O 3 (s) + 2 OH - Reduction: NH 4 + + OH - -> NH 3 (g) + H 2 O(l) Acid-base reaction: NH 3 + Zn 2+ (aq) + Cl - -> [Zn(NH 3 ) 2 ]Cl 2 (s) Precipitation reaction:
  • 4. Alkaline Dry Cell Slide of 54 Zn 2+ (aq) + 2 OH - -> Zn (OH) 2 (s) Zn(s) -> Zn 2+ (aq) + 2 e - Oxidation reaction can be thought of in two steps: 2 MnO 2 (s) + H 2 O(l) + 2 e - -> Mn 2 O 3 (s) + 2 OH - Reduction: Zn (s) + 2 OH - -> Zn (OH) 2 (s) + 2 e -
  • 5. Lead-Acid (Storage) Battery
    • The most common secondary battery.
    Slide of 54
  • 6. Lead-Acid Battery Slide of 54 PbO 2 (s) + 3 H + (aq) + HSO 4 - (aq) + 2 e - -> PbSO 4 (s) + 2 H 2 O(l) Oxidation: Reduction: Pb (s) + HSO 4 - (aq) -> PbSO 4 (s) + H + (aq) + 2 e - PbO 2 (s) + Pb(s) + 2 H + (aq) + HSO 4 - (aq) -> 2 PbSO 4 (s) + 2 H 2 O(l) E° cell = E ° PbO 2 /PbSO 4 - E ° PbSO 4 /Pb = 1.74 V – (-0.28 V) = 2.02 V
  • 7. The Silver-Zinc Cell: A Button Battery Slide of 54 Zn(s),ZnO(s)|KOH(sat’d)|Ag 2 O(s),Ag(s) Zn(s) + Ag 2 O(s) -> ZnO(s) + 2 Ag(s) E cell = 1.8 V
  • 8. The Nickel-Cadmium Cell Slide of 54 Cd(s) + 2 NiO(OH)(s) + 2 H 2 O(L) -> 2 Ni(OH) 2 (s) + Cd(OH) 2 (s)
  • 9. 20-7 Electrolysis: Causing Non-spontaneous Reactions to Occur Slide of 54 Galvanic Cell: Zn(s) + Cu 2+ (aq) -> Zn 2+ (aq) + Cu(s) E O 2 /OH - = 1.103 V Electolytic Cell: Zn 2+ (aq) + Cu(s) -> Zn(s) + Cu 2+ (aq) E O 2 /OH - = -1.103 V
  • 10. Predicting Electrolysis Reaction
    • An Electrolytic Cell
      • e - is the reverse of the voltaic cell.
      • Battery must have a voltage in excess of 1.103 V in order to force the non-spontaneous reaction.
    Slide of 54
  • 11. Complications in Electrolytic Cells
    • Overpotential.
    • Competing reactions.
    • Non-standard states.
    • Nature of electrodes.
    Slide of 54
  • 12. Quantitative Aspects of Electrolysis Slide of 54 1 mol e - = 96485 C Charge (C) = current (C/s)  time (s) n e - = I  t F