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Coal and Petroleum

CBSE Class 8 Science • Chapter 6 • Detailed Master Notes

Chapter Overview

This chapter focuses on the energy that powers our world. We will study natural resources, the difference between renewable and non-renewable energy, and deep dive into fossil fuels like Coal, Petroleum, and Natural Gas.

6.1 Natural Resources & Energy

A good source of energy can provide an adequate amount of energy in a convenient form over a long period of time.

Natural Resources: Anything present in the environment that can be used by human beings to meet their needs.
Examples: Sunlight, wind, soil, minerals, coal, and petroleum.

Classification of Natural Resources

Inexhaustible (Renewable) Resources	Exhaustible (Non-Renewable) Resources
Resources that are present in unlimited quantity in nature. They are not likely to be exhausted by human activities.	Resources whose amount in nature is limited. They can be completely exhausted by human activities over time.
Examples: Sunlight, wind, water, and biomass.	Examples: Coal, petroleum, natural gas, minerals, and forests.

Topic Practice: Resources

Q1. Why is sunlight considered an inexhaustible natural resource?

Ans: Sunlight is generated by the sun continuously and is abundantly present in unlimited quantities. Our daily consumption does not deplete it.

6.2 Fossil Fuels

What are Fossil Fuels?
Fossil fuels are combustible fuels formed from the slow natural decomposition of buried dead organisms (plants and animals) trapped beneath the Earth's crust over millions of years under extreme heat and pressure.

Because the process takes millions of years, these are Exhaustible Natural Resources. The three main fossil fuels are Coal, Petroleum, and Natural Gas.

AI Image Prompt: A 3D cross-section diagram of the Earth. Show three layers vertically. Top layer: A prehistoric swamp forest with fern trees. Middle layer: Thick brown sediment layers and deeply buried ancient decaying logs. Bottom layer: Intense red magma heat radiating upward, compressing black carbon coal seams and pools of trapped liquid petroleum oil under grey rock layers.

6.3 Coal and its Products

Coal is a hard, black combustible mineral rock that consists primarily of carbon.

A. How Coal was Formed (Carbonisation)

About 300 million years ago, the earth had dense forests in low-lying wetland areas.
Due to natural processes like floods, these forests got buried under soil.
As more soil deposited over them, they were compressed deeper.
In the absence of air, subjected to high temperature and high pressure, the dead plants slowly converted to coal.
Definition: The slow process of the conversion of dead vegetation into coal is called Carbonisation.

B. Useful Products from Coal

When coal is heated in the absence of air (Destructive Distillation), we obtain useful products:

1. Coke: A tough, porous, and black solid substance. It is an almost pure form of carbon.
Uses: Used in the manufacture of steel and in the extraction of many metals.
2. Coal Tar: A black, thick liquid with an unpleasant smell.
Uses: Used to manufacture synthetic dyes, drugs, explosives, perfumes, plastics, and paints. Naphthalene balls are also obtained from coal tar.
3. Coal Gas: A flammable gas obtained during the processing of coal to get coke.
Uses: Used mainly as a fuel in heavy industries situated near coal processing plants.

Topic Practice: Coal

Q1. What is carbonisation?

Ans: The slow natural chemical process involving the deep underground conversion of dead vegetation into coal under extreme heat and pressure over millions of years.

6.4 Petroleum

Petroleum is a dark, oily liquid with an unpleasant odour. It is known as "Black Gold" due to its immense commercial importance.

A. Formation of Petroleum

Unlike coal (formed from land plants), petroleum was formed from tiny organisms living in ancient seas and oceans.
As these organisms died, their bodies settled at the bottom of the sea.
They gradually got covered with layers of sand and clay over time.
Over millions of years, the absence of air, combined with high temperature and pressure, transformed these dead sea organisms into liquid petroleum and natural gas.

B. Refining of Petroleum

Raw crude petroleum pumped from the ground is a complex mixture of constituents like petroleum gas, petrol, diesel, lubricating oil, and paraffin wax. It cannot be used directly in this crude form.

Refining: The process of separating the various useful fractions of crude petroleum using fractional distillation is called refining. This is done in petroleum refineries.

Fraction of Petroleum	Major Uses
LPG (Liquefied Petroleum Gas)	Fuel for domestic home cylinders and industry.
Petrol	Motor fuel for cars and bikes, aviation fuel, and dry cleaning solvent.
Kerosene	Fuel for domestic stoves, lamps, and jet aircraft.
Diesel	Fuel for heavy motor vehicles (trucks, tractors) and electric generators.
Lubricating Oil	Used for lubrication inside machines to reduce friction.
Paraffin Wax	Used in making ointments, candles, and petroleum jelly.
Bitumen	A black fraction used for making paints and surfacing new asphalt roads.

6.5 Natural Gas

Natural gas is an important fossil fuel because it is easy to transport through underground pipelines.

Compressed Natural Gas (CNG): Natural gas is stored under high pressure. CNG is used for power generation and as a very clean fuel for transport vehicles because it is less polluting and leaves no ash on burning.

6.6 The Consequences of Over-Extraction

The known reserves of coal and petroleum will last only a few hundred years at the current rate of consumption. Secondly, burning these fuels is a major cause of air pollution and strongly linked to Global Warming.

PCRA Guidelines for conserving fuel: The Petroleum Conservation Research Association (PCRA) advises people how to save petrol/diesel while driving:

Drive at a constant and moderate speed as far as possible.
Switch off the engine at traffic lights or at a place where you have to wait.
Ensure correct tyre pressure.
Ensure regular maintenance of the vehicle.

Topic Practice: Conservation

Q1. Why is CNG considered a better fuel than petrol for automobiles?

Ans: CNG is an extensively cleaner fuel because it produces significantly fewer harmful polluting gases on burning. It burns completely and leaves no ash behind.