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Batteries

Batteries. Galvanic Cell. Any battery or cell that is used as a source of electrical energy is basically a galvanic cell where the chemical energy of the redox reaction is converted into electrical energy. Batteries.

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Batteries

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  1. Batteries Galvanic Cell Any battery or cell that is used as a source of electrical energy is basically a galvanic cell where the chemical energy of the redox reaction is converted into electrical energy.

  2. Batteries Batteries, constructed from one or more galvanic cells, are usually compact and sturdy devices that are easily stored and utilized. Types of Batteries

  3. Primary batteries A primary battery is a portable galvanic cell that is not rechargeable. Examples: Dry cell Dry cell (Leclanche cell) Mercury cell Mercury cell

  4. Dry cell (Leclanche cell) A flashlight battery, or dry cell, is constructed with a zinc shell that serves as the anode; a graphite rod which serves as the cathode; and a moist mixture of ammonium chloride {NH4Cl}, zinc chloride {ZnCl2}, and manganese dioxide {MnO2}.

  5. Dry cell (Leclanche cell) The overall reaction occurring in the dry cell produces 1.5 volts.

  6. Dry cell (Leclanche cell) These batteries tend to have poor shelf life because the zinc anode will slowly react with ammonium ions even when not connected to an external circuit. Storing a dry cell in a refrigerator will decrease the rate of this reaction and extend the shelf life of the battery significantly. The dry cell is used in transistors and clocks.

  7. Mercury cell In mercury cells, mercury amalgam act as anode and a paste of HgO and carbon as the cathode. The electrolyte is a paste of KOH and ZnO.

  8. Mercury cell Electrode reactions involved in Mercury cell: At Anode: Zn(Hg) + 2OH- ---> ZnO + H2O + 2e- At Cathode: HgO + H2O + 2e----> Hg + 2OH- Zn(Hg) + HgO ---> Hg + ZnO Overall Reaction: The cell potential is approximately 1.35 V.

  9. Mercury cell These cells contain mercury, which in certain forms is highly toxic to humans and animals. Mercury batteries were used in the shape of button cells for watches, hearing aids, and calculators, and in larger forms for other applications.

  10. Secondary batteries A secondary battery is a portable voltaic cell that is rechargeable. Examples: Lead storage battery Lead storage battery Nickel cadmium cell Nickel cadmium cell

  11. Lead storage battery The electrodes of the cells in a lead storage battery consist of lead grids. The openings of the anodic grid is filled with spongy (porous) lead. The openings of the cathodic grid is filled with lead dioxide {PbO2}. Dilute sulphuricacid {H2SO4} serves as the electrolyte.

  12. Lead storage battery When the battery is delivering a current, i.e. discharging, the lead at the anode is oxidized: Because the lead ions are in the presence of aqueous sulphateions (from the sulfuric acid), insoluble lead sulphateprecipitates onto the electrode. The overall reaction at the anode is therefore:

  13. Lead storage battery Electrons that flow from the anode simultaneously reduce the lead dioxide at the cathode: The lead ions that are formed react with aqueous sulphateions to form insoluble lead sulphateon the electrode, and the overall reaction at the cathode is:

  14. Lead storage battery Overall equation for lead storage battery when it is discharging: Pb + PbO2 + 2H2SO4 → 2PbSO4+ 2H2O On charging the battery, the reaction is reversed and PbSO4 on anode and cathode is converted into Pb and PbO2 , respectively. Lead storage battery is commonly used in automobiles and invertors.

  15. Nickel Cadmium cell Nickel cadmium cell which has longer life than the lead storage cell but more expensive to manufacture. Nickel-cadmium cells have an anode (negative) in cadmium hydroxide and a cathode (positive) in nickel hydroxide, immersed in an alkaline solution (electrolyte) comprising potassium, sodium and lithium hydroxides. The cells are rechargeable and deliver a voltage of 1.2 V during discharge. 

  16. Nickel Cadmium cell The overall reaction during discharging of Nickel cadmium cell is: Cd +2Ni(OH)3 → CdO +2Ni(OH)2 +H2O Nickel cadmium batteries are used in emergency lighting, standby power and uninterruptible power supplies.

  17. Fuel cells Galvanic cells that are designed to convert the energy of combustion of fuels like hydrogen, methane, methanol, etc. directly into electrical energy are called fuel cells.

  18. Fuel cells Anode: 2H2(g) + 4OH- (aq) ⎯→ 4H2O(l) + 4e- Cathode: O2(g) + 2H2O(l) + 4e- ⎯→ 4OH- (aq) Overall Reaction: 2H2(g) + O2(g) ⎯→ 2 H2O (l)

  19. Fuel cells Fuel cell was used for providing electrical power in the Apollo space programme. The water vapoursproduced during the reaction were condensed and added to the drinking water supply for the astronauts.

  20. Fuel cells The fuel cell runs continuously as long as the reactants are supplied. These cells produce electricity with an efficiency of about 70 % compared to thermal plants whose efficiency is about 40%. Fuel cells have been used in automobiles on an experimental basis. These cells are pollution free and in view of their future importance, a variety of fuel cells have been fabricated and tried.

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