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Voltaic Cells as Energy Sources

Voltaic Cells as Energy Sources. Dry Cells. A compact, portable electrical energy source A voltaic cell in which the electrolyte is a paste Example: a flashlight battery/alkaline battery Starts out at a certain voltage but decreases steadily over time. Alkaline Battery.

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Voltaic Cells as Energy Sources

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  1. Voltaic Cells as Energy Sources

  2. Dry Cells • A compact, portable electrical energy source • A voltaic cell in which the electrolyte is a paste • Example: a flashlight battery/alkaline battery • Starts out at a certain voltage but decreases steadily over time

  3. Alkaline Battery

  4. Alkaline Battery Reactions • Oxidation: Zn(s)  Zn+2(aq) + 2e- • Reduction: 2MnO2(s) + 2NH4+ + 2e-  Mn2O3(s) + 2NH3 (aq) + H2O(l)

  5. Lead Storage Battery • Example: car battery • A group of voltaic cells connected together • Recharging a battery is a reverse reaction to the charging of one, and is not a spontaneous reaction • Each recharge causes small amounts of lead sulfate fall from the electrodes and collect on the bottom of the cell • Eventually, there is not enough lead sulfate to recharge the battery and must be replaced

  6. Lead Storage Battery

  7. Lead Storage Reactions Oxidation: Pb(s) + SO42- (aq)  PbSO4 (s) + 2e- Reduction: PbO2(s) + 4H+(aq) + SO42-(aq) + 2e- PbSO4(s) + 2H2O(l)

  8. Fuel Cells Cells with renewable electrodes Contains a fuel substance that undergoes oxidation and continuously obtains electrical energy Emit no air pollutants and are quieter and more cost-effective than traditional generators

  9. Example of a Fuel Cell Hydrogen-oxygen fuel cell Three compartments separated by two electrodes of carbon Oxygen (the oxidizer) is fed into the cathode Hydrogen (the fuel) is fed into the anode Central compartment contains potassium hydroxide

  10. Fuel Cell

  11. Fuel Cell Reactions Oxidation: 2H2(g) + 4OH-(aq)  4H2O(l) + 4e- Reduction: O2(g) + 2H2O(l) + 4e- 4OH-(aq)

  12. Uses of Fuel Cells • Energy on spacecrafts • Continuous energy source • No pollutants released • Can drink the water produced by the fuel cells • Submarines • Future for cars?

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