NCERT Class 8 Science Chapter 5 - Coal and Petroleum Notes

Chapter 5 - Coal and Petroleum Notes

1. Resources
• We use various materials for our basic needs. Some of them already exist in nature while some resources have been made by humans.
• Natural resources are the resources that are drawn from nature and are used without much modification. Example: Water, Soil, etc.

2. Classification of Resources
In the light of the availability of various resources in nature, natural resources can be broadly classified into two kinds:
• Inexhaustible Natural Resources: These resources are present in unlimited quantity in nature and are not likely to be exhausted by human activities. Example: sunlight, air etc.
• Exhaustible Natural Resources: The amount of these resources in nature is limited. They can be exhausted by human activities. Example: forests, wildlife, minerals, coal, petroleum, natural gas etc.
Some exhaustible natural resources like coal, petroleum and natural gas were formed from the dead remains of living organisms (fossils). So, these are all known as fossil fuels.

3. Coal
• Coal is as hard as stone and is black in colour.
• Coal is one of the fuels used to cook food.
• Earlier, it was used in railway engines to produce steam to run the engine.
It is also used in thermal power plants to produce electricity. Coal is also used as a fuel in various industries.

4. Story of Coal
• Many 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.
• The temperature also rose as they sank deeper and deeper. Under high pressure and high temperature, dead plants got slowly converted to coal.
• As coal contains mainly carbon, the slow process of conversion of dead vegetation into coal is called carbonisation.
• Since it was formed from the remains of vegetation, coal is also called a fossil fuel.
• When heated in air, coal burns and produces mainly carbon dioxide gas. Coal is processed in industry to get some useful products such as coke, coal tar and coal gas.

5. Some useful products extracted from coal
• Coke: It is a tough, porous and black substance. It is an almost pure form of carbon. Coke is used in the manufacture of steel and in the extraction of many metals.
• Coal Tar: It is black, thick liquid with an unpleasant smell. It is a mixture of about 200 substances. Products obtained from coal tar are used as starting materials for manufacturing various substances used in everyday life and in industry, like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, etc. Also, naphthalene balls used to repel moths and other insects are also obtained from coal tar.
• Coal Gas: Coal gas is obtained during the processing of coal to get coke. It is used as a fuel in many industries situated near the coal processing plants.

6. Petroleum
• Petrol is used as a fuel in light automobiles such as motor cycles/scooters and cars. Heavy motor vehicles like trucks and tractors run on diesel.
• Petrol and diesel are obtained from a natural resource called petroleum.
• The word petroleum is derived from petra (rock) and oleum (oil) as it is mined from between the rocks under Earth.

7. Story of Petroleum
• 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, absence of air, high temperature and high pressure transformed the dead organisms into petroleum and natural gas.

8. Refining of Petroleum
• Petroleum is a dark oily liquid. It has an unpleasant odour.
• It is a mixture of various constituents such as petroleum gas, petrol, diesel, lubricating oil, paraffin wax, etc.
• The process of separating the various constituents/fractions of petroleum is known as refining. It is carried out in a petroleum refinery.

9. Constituents of Petroleum and their uses
• Petroleum Gas in Liquid form (LPG): Fuel for home and industry
• Petrol: Motor fuel, Aviation fuel, solvent for dry cleaning
• Kerosene: Fuel for stoves, lamps and for jet aircrafts
• Diesel: Fuel for heavy motor vehicles, electric generators
• Lubricating oil: Lubrication
• Paraffin wax: Ointments, candles, Vaseline etc.
• Bitumen: Paints, road surfacing

10. Natural Gas
• Natural gas is a very important fossil fuel because it is easy to transport through pipes.
• Natural gas is stored under high pressure as compressed natural gas (CNG).
• CNG is used for power generation. It is now being used as a fuel for transport vehicles because it is less polluting. It is a cleaner fuel.
• CNG can be used directly for burning in homes and factories where it can be supplied through pipes. Such a network of pipelines exists in Vadodara (Gujarat), some parts of Delhi and other places.
• Natural gas is also used as a starting material for the manufacture of a number of chemicals and fertilisers.
• In India, natural gas has been found in Tripura, Rajasthan, Maharashtra and in the Krishna Godavari delta.

11. Some Natural Resources are limited
• Some natural resources are exhaustible like fossil fuels, forests, minerals etc. Coal and petroleum are fossil fuels.
• It required the dead organisms millions of years to get converted into these fuels. On the other hand, the known reserves of these will last only a few hundred years.
• Burning of these fuels is a major cause of air pollution. Their use is also linked to global warming. It is therefore necessary that we use these fuels only when absolutely necessary.
• This will result in better environment, smaller risk of global warming and their availability for a longer period of time. In India, the Petroleum Conservation Research Association (PCRA) advises people how to save petrol/diesel while driving. Their tips are
→ 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 vehicles

12. These days, bitumen, a petroleum product, is used in place of coal-tar for metalling the roads.

13. Coal gas was used for street lighting for the first time in London in 1810 and in New York around 1820. Now a days, it is used as a source of heat rather than light.

14. The world’s first oil well was drilled in Pennsylvania, USA, in 1859. Eight years later, in 1867, oil was struck at Makum in Assam. In India, oil is found in Assam, Gujarat, Mumbai High and in the river basins of Godavari and Krishna.

15. Many useful substances are obtained from petroleum and natural gas. These are termed as ‘Petrochemicals’. These are used in the manufacture of detergents, fibres (polyester, nylon, acrylic etc.), polythene and other man-made plastics. Hydrogen gas obtained from natural gas, is used in the production of fertilisers (urea). Due to its great commercial importance, petroleum is also called ‘black gold’.

16. Can coal, petroleum and natural gas be prepared in the laboratory from dead organisms?
No, it is difficult to prepare coal, petroleum and natural gas in laboratory from dead organisms because their formation is a very slow process and conditions for their formation cannot be created in the laboratory.

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