Electrochemistry & Fuels Overview

Lead Acid Storage Cell

The lead-acid storage cell is a rechargeable electrochemical cell widely used in automobiles. It consists of a lead (Pb) anode, a lead dioxide (PbO₂) cathode, and a sulfuric acid (H₂SO₄) electrolyte.

Discharge: Pb + PbO₂ + 2H₂SO₄ → 2PbSO₄ + 2H₂O

During charging, the reaction is reversed by an external current source.

Leclanché Cell

The Leclanché cell is a primary (non-rechargeable) cell with a zinc (Zn) anode, a carbon rod cathode surrounded by manganese dioxide (MnO₂), and an ammonium chloride (NH₄Cl) electrolyte paste.

Overall reaction: Zn + 2MnO₂ + 2NH₄Cl → ZnCl₂ + Mn₂O₃ + 2NH₃ + H₂O

Calorific Value of Fuels

The calorific value is the amount of heat energy released when a unit mass of fuel is completely burnt.

Calorific Value (CV) = Heat produced / Mass of fuel burnt (J/kg or kJ/mol)

It is determined using a bomb calorimeter and is critical for fuel efficiency assessment.

Proximate and Ultimate Analysis of Coals

Proximate Analysis measures:

Moisture content
Volatile matter
Ash content
Fixed carbon

Ultimate Analysis determines elemental composition:

Carbon (C)
Hydrogen (H)
Nitrogen (N)
Sulfur (S)
Oxygen (O)

Fuel Cells

A fuel cell directly converts chemical energy of fuel into electrical energy through redox reactions without combustion.

Example: Hydrogen-oxygen fuel cell:

Anode: 2H₂ → 4H⁺ + 4e⁻
Cathode: O₂ + 4H⁺ + 4e⁻ → 2H₂O

Biofuels

Biofuels are derived from renewable biological sources such as plants and algae. Examples include bioethanol (C₂H₅OH) and biodiesel (fatty acid methyl esters).

Advantages: Renewable, biodegradable, reduced greenhouse gas emissions. Disadvantages: Land use issues, possible competition with food production.

Electrochemistry and Fuels - 3

Study Notes