1. What are fossil fuels?

Fossil fuels are energy-rich substances formed from the remains of dead plants and animals buried deep inside the earth millions of years ago. The two most important fossil fuels discussed in this chapter are coal and petroleum. They have stored chemical energy which is released when they are burned.

2. Formation of Coal

Coal forms from the remains of plants that lived in swampy regions during the Carboniferous period and later eras. Over millions of years, layers of plant debris were buried under sediments. Heat, pressure and bacterial action transformed this organic matter into peat and then into different types of coal through a process called carbonisation.

1. Peat: Partially decayed plant matter — lowest carbon content.
2. Lignite (brown coal): Low-grade coal with more carbon than peat.
3. Bituminous coal: Higher carbon content, used for heating and power generation.
4. Anthracite: Highest carbon content, burns cleanly with high heat output.

As the rank of coal increases (peat → anthracite), the percentage of carbon increases while moisture and volatile matter decrease. Coal contains carbon, hydrogen, oxygen and impurities like sulfur and ash-forming minerals.

3. Uses and disadvantages of coal

Coal is primarily used as a fuel for electricity generation and in industries such as steel manufacturing. It is also used in domestic heating in some regions and as a raw material for manufacture of coke and coal gas.

• Uses: Thermal power plants, production of coke for metallurgy, manufacture of certain chemicals and gas.
• Disadvantages: Produces smoke and harmful gases like carbon monoxide and sulfur dioxide on burning, contributes to air pollution and acid rain; mining leads to land degradation and safety hazards.

4. Petroleum: origin and crude oil

Petroleum (crude oil) is formed from the remains of tiny marine organisms (plankton) and plants that settled at the bottom of ancient seas. Buried under sediments, they underwent chemical transformation under heat and pressure to form petroleum and natural gas. Crude oil is a complex mixture of hydrocarbons of varying chain length and molecular structure.

5. Fractional distillation of petroleum

To separate useful products from crude oil, the process of fractional distillation is used in refineries. Crude oil is heated and fed into a tall fractionating column. Because different hydrocarbons have different boiling points, they condense at different levels in the column and are collected as fractions.

Important fractions (from top to bottom):

• Petrol (gasoline): Lightest fraction, used in petrol engines.
• Naphtha: Used as a feedstock for petrochemicals.
• Kerosene: Used as aviation fuel and for heating.
• Diesel: Used in diesel engines and some generators.
• Lubricating oil & waxes: Used for lubrication and manufacturing.
• Bitumen: Heaviest fraction — used for road surfacing and roofing.

6. Natural gas and LPG

Natural gas is often found with petroleum deposits and mainly consists of methane (CH₄). It is a clean fuel used for cooking, heating and electricity generation. Liquefied Petroleum Gas (LPG) is a mixture of propane and butane and is commonly used as a domestic fuel. LPG is stored under pressure as a liquid and is transported in cylinders.

7. Uses of petroleum products

Petroleum fractions are vital in daily life and industries. Key uses include:

• Fuel for transport (petrol, diesel, kerosene)
• Cooking and heating (LPG)
• Lubricants for machines
• Raw materials for petrochemical industry (plastics, synthetic fibres, detergents, paints)
• Bitumen for road construction

8. Environmental concerns

Burning fossil fuels releases carbon dioxide (CO₂) — a greenhouse gas — and other pollutants that contribute to global warming, smog and respiratory diseases. Oil spills and accidental leakage cause severe harm to marine ecosystems. Mining and drilling can disturb habitats and pollute water sources.

9. Safety and precautions

Fossil fuels are flammable and must be handled carefully. Safety precautions: avoid open flames near storage areas, ensure proper ventilation when using fuels indoors, follow cylinder handling guidelines for LPG, and follow environmental regulations during extraction and transport.

10. Exam-oriented quick facts (for revision)

• Coal: formed from plant remains — types: peat, lignite, bituminous, anthracite.
• Petroleum: formed from marine organisms — complex hydrocarbon mixture.
• Fractional distillation separates crude oil into useful fractions based on boiling points.
• Natural gas is mostly methane; LPG contains propane and butane.
• Major uses: fuels, lubricants, road materials, petrochemicals for plastics and fibres.
• Environmental impact: air pollution, greenhouse gases, oil spills, land degradation.

11. Practice questions (short)

1. Define coal and describe its formation in brief.
2. List two major differences between bituminous coal and anthracite.
3. Explain fractional distillation with a simple labelled diagram (draw in exam).
4. Mention three important uses of petroleum fractions.
5. Give two environmental concerns associated with fossil fuel use.

12. Final tips for board exam preparation

• Learn the formation steps and types of coal and remember examples.
• Practice drawing and labelling the fractionating column and remembering which fraction is collected at which level.
• Memorise uses of each major petroleum fraction and common safety points about LPG.
• Prepare 2–3 lines on environmental impacts and conservation measures — these are common short-answer questions.