CBSE Class 8 Science Chapter 5: Coal and Petroleum Revision Notes

Classification of Natural Resources

Important Technical Terms & Glossary

Fossil Fuels

Natural fuels formed over millions of years from the dead remains of living organisms buried deep under the Earth.

Carbonisation

The slow chemical process by which dead vegetation is converted into coal under high pressure and high temperature inside the Earth.

Petroleum

A dark, oily liquid natural resource formed from dead organisms in the sea, consisting of a mixture of various hydrocarbons.

Fractional Distillation

The industrial process of separating different constituents or fractions of petroleum based on their boiling points.

Petrochemicals

Useful chemical substances obtained from petroleum and natural gas, used to manufacture detergents, synthetic fibres, and plastics.

CNG (Compressed Natural Gas)

Natural gas stored under high pressure, used as a cleaner, less polluting fuel for transport vehicles.

Formation of Coal and Petroleum

Fossil fuels require specific environmental conditions to form. About 300 million years ago, the Earth had dense forests in low-lying wetland areas. Due to natural processes like flooding, these forests got buried under the soil. As more soil deposited over them, they were compressed. Under high pressure and high temperature deep inside the earth, the buried dead plants slowly got converted into coal. This slow process of conversion of dead vegetation into coal is called carbonisation.

Similarly, petroleum was formed from organisms living in the sea. As these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay. Over millions of years, in the absence of air, under high temperature and high pressure, these dead organisms transformed into petroleum and natural gas. Because they are lighter than water, oil and gas deposits float above the underground water layer.

Products of Coal Processing (Destructive Distillation)

1. — Coal is processed in industries in the absence of air (destructive distillation) to obtain useful products.
2. — A tough, porous, and black substance which is an almost pure form of carbon. It is primarily used in the manufacture of steel and extraction of metals.
3. — A thick black liquid with an unpleasant smell. It is a mixture of about 200 substances, used as a starting material for dyes, synthetic fibers, drugs, and explosives (though bitumen has now replaced it for surfacing roads).
4. — Obtained during the processing of coal to get coke. It is used as a fuel in many industries situated near coal processing plants.

Constituents of Petroleum and Their Uses

• LPG (Liquefied Petroleum Gas): Fuel for home and industry.
• Petrol: Aviation fuel, motor fuel, solvent for dry cleaning.
• Kerosene: Fuel for stoves, lamps, and jet aircraft.
• Diesel: Fuel for heavy motor vehicles, electric generators.
• Lubricating Oil: Used for reducing friction in machines (lubrication).
• Paraffin Wax: Used to make ointments, candles, vaseline, etc.
• Bitumen: Used for paints and road surfacing (replaces traditional coal tar).

Exam Traps & Smart Revision Tips

1. Coal Tar vs Bitumen: Boards frequently ask what is currently used for surfacing roads. Always write Bitumen (a petroleum product), as it has largely replaced Coal Tar (a coal product).
2. Why Petroleum is called 'Black Gold': Because of its immense commercial and economic value across multiple chemical and transport industries.
3. PCRA Full Form & Guidelines: Be ready with the full form: Petroleum Conservation Research Association. Remember their advice: Drive at constant/moderate speed, switch off engine at traffic lights, ensure correct tyre pressure, and regular vehicle maintenance.

Practice Questions with Solutions

• Q: Why are coal and petroleum classified as exhaustible natural resources? A: They are classified as exhaustible because they require millions of years to form from dead organic matter, and their current rate of consumption by humans is far faster than their rate of natural formation.
• Q: Explain the process of carbonisation. A: Carbonisation is the slow chemical process of conversion of dead vegetation into coal under the conditions of high temperature, high pressure, and absence of air deep inside the Earth.
• Q: Name the petroleum product used for surfacing roads today. A: Bitumen is the petroleum product currently used for surfacing roads.
• Q: What is the main advantage of using CNG over petrol or diesel? A: CNG is a cleaner burning fuel that produces very little residue or harmful gases, making it significantly less polluting than petrol or diesel.

Frequently Asked Questions