Chemistry class 12th Batteries_Class_12_Chemistry

Batteries - Class 12 Chemistry


### Introduction to Batteries
A battery is an electrochemical device that converts chemical energy into electrical energy. It
consists of one or more
electrochemical cells, each containing two electrodes (anode and cathode) and an electrolyte.


### Types of Batteries
Batteries are classified into two main types:
1. **Primary Batteries** - Non-rechargeable, used once and discarded.
2. **Secondary Batteries** - Rechargeable, can be used multiple times.


### Primary Batteries
These batteries undergo irreversible chemical reactions and cannot be recharged.


#### 1. Dry Cell (Leclanché Cell)
- **Anode:** Zn (Zinc)
- **Cathode:** Carbon (Graphite rod)
- **Electrolyte:** NH4Cl + ZnCl2 paste
- **Reactions:**
- At Anode: Zn -> Zn2+ + 2e-
- At Cathode: MnO2 + NH4+ + e- -> Mn(OH)3 + NH3
- **Uses:** Flashlights, remote controls, clocks.


#### 2. Mercury Cell
- **Anode:** Zn-Hg amalgam
- **Cathode:** HgO + graphite
- **Electrolyte:** KOH-ZnO paste
- **Uses:** Hearing aids, watches.


### Secondary Batteries
These are rechargeable and widely used in modern devices.


#### 1. Lead-Acid Battery
- **Anode:** Pb (Lead)
- **Cathode:** PbO2 (Lead dioxide)
- **Electrolyte:** H2SO4 (Sulfuric acid)