18.5 batteries

• a battery is a galvanic cell or a series of cells used as a source of current at constant voltage
• a dry cell battery is used in calculators, clocks, toys, etc.
• dry cell

  anode: Zn -> Zn2+ + 2e-

  cathode: 2e- + 2NH+ + 2MnO2 -> Mn2O3 + 2NH3 + H2

  Zn + 2NH+ + 2MnO2 -> Zn2+ + 2NH3 + H2O + Mn2O3

  voltage: 1.5V
• lead storage batteries are used in cars
• there are 6 cells in lead storage batteries, which form a series in which voltages add from one to the next
• lead storage battery

  anode: Pb + SO42- -> PbSO4 + 2e-

  cathode: 2e- + PbO2 + 4H+ + SO42- -> PbSO4 + 2H2O

  Pb + PbO2 + 4H+ + 2SO42- -> 2PbSO4 + 2H2O

  voltage: each cell = 2V so overall is 12V
• lithium ion batteries are used in pacemakers, cameras, cellphones, and laptops
• lithium ion batteries do not have water in them
• lithium ion battery

  anode: Li -> Li+ + e-

  cathode: e- + Li+ + CoO2 -> LiCoO2

  Li + CoO2 -> LiCoO2

  voltage: 3.4V
• fuel cells are used in backup power supplies and space vehicles
• fuel cells are galvanic cells that require a continuous supply of reactants to keep working
• fuel cell

  anode: 2H2 + 4OH- -> 4H2O + 4e-

  cathode: 4e- + O2 + 2H2O -> 4OH-

  2H2 + O2 -> 2H2O

  voltage: 1.23V