A battery is a device that stores and converts chemical energy into electrical energy by means of an electrochemical reaction. Batteries are commonly used to power various electronic devices such as laptops, mobile phones, cameras, and automobiles.There are various types of batteries, but two common types are dry cell batteries and lead storage batteries.
Dry-Cell Batteries Dry-cell batteries are used in calculators, watches, flashlights, and battery-operated toys. The term dry cell describes a battery that uses a paste rather than an aqueous solution. Dry cells can be acidic or alkaline.
In an acidic dry cell, the anode is a zinc metal case that contains a paste of MnO2, NH4Cl, ZnCl2, H2O, and starch. Within this MnO2 electrolyte mixture is a graphite cathode.
A basic or alkaline battery has similar components except that NaOH or KOH replaces the NH4Cl electrolyte. Under basic conditions, the product of oxidation is zinc oxide (ZnO). Alkaline batteries tend to be more expensive, but they last longer and produce more power than acidic dry-cell batteries.
Anode (oxidation): Zn(s) → Zn2+(aq) + 2 e−
Cathode (reduction): 2 e− + 2MnO2(s) + 2NH4 +(aq) → Mn2O3(s) + 2NH3(aq) + H2O(l)
Overall cell-reaction: Zn(s) + 2MnO2(s) + 2NH4 +(aq) → Zn2+(aq) + Mn2O3(s) + 2NH3(aq) + H2O(l)
The tiny batteries found in hearing aids, calculators, and camera flashes are mercury batteries, as shown. The cathode half-reaction is described by the following equation:
Hg+2O(s) + H2O(l) + 2e- → Hg0 (l) + 2OH–(aq)
A lead storage battery is used to operate the electrical system in a car. We need a car battery to start the engine, turn on the lights, or operate the radio. If the battery runs down, the car won’t start and the lights won’t turn on. A car battery or a lead storage battery is a type of voltaic cell. In a typical 12-V battery, there are six voltaic cells linked together. Each of the cells consists of a lead (Pb) plate that acts as the anode and a lead (IV) oxide (PbO2) plate that acts as the cathode. Both half-cells contain a sulfuric acid (H2SO4) solution. When the car battery is producing electrical energy (discharging), the following half-reactions take place:
Anode (oxidation): Pb(s) + SO4 2-(aq) → PbSO4(s) + 2e−
Cathode (reduction): 2e− + 4H+(aq) + PbO2(s) + SO4 2-(aq) → PbSO4(s) + 2H2O(l)
Overall cell-reaction: 4H+(aq) + Pb(s) + PbO2(s) + 2SO4 2-(aq) ) → 2PbSO4(s) + 2H2O(l)
