Dry CellsDry 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 BatteryAlkaline Battery
Alkaline Battery ReactionsAlkaline Battery Reactions Oxidation: Zn(s) Zn +2 (aq) + 2e - Reduction: 2MnO 2 (s) + 2NH e - Mn 2 O 3 (s) + 2NH 3 (aq) + H 2 O(l)
Lead Storage BatteryLead 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
Lead Storage BatteryLead Storage Battery
Lead Storage ReactionsLead Storage Reactions Oxidation: Pb(s) + SO 4 2- (aq) PbSO 4 (s) + 2e - Reduction: PbO 2 (s) + 4H + (aq) + SO 4 2- (aq) + 2e - PbSO 4 (s) + 2H 2 O(l)
Fuel CellsFuel 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
Example of a Fuel CellExample 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
Fuel CellFuel Cell
Fuel Cell ReactionsFuel Cell Reactions Oxidation: 2H 2 (g) + 4OH - (aq) 4H 2 O(l) + 4e - Reduction: O 2 (g) + 2H 2 O(l) + 4e - 4OH - (aq)
Uses of Fuel CellsUses 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?