Chapter Notes - Coal & Petroleum Class 8 Notes | EduRev

Science Class 8

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Class 8 : Chapter Notes - Coal & Petroleum Class 8 Notes | EduRev

The document Chapter Notes - Coal & Petroleum Class 8 Notes | EduRev is a part of the Class 8 Course Science Class 8.
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Natural Resources
Resources supplied by nature are called natural resources. The sun, air, water, soil, trees and forests, wildlife, coal, petroleum, natural gas and minerals are all natural resources. Many industries, like fishing, mining, hunting, agriculture and forestry, revolve around the sensible use of natural resources. Natural resources are classified as renewable and non-renewable resources. Renewable resources are those that are present in unlimited quantity in nature or those that will replace themselves over time. 

These resources are not likely to be exhausted by human activities. As they are unlimited, they are also called inexhaustible resources. Non-renewable resources are those that are limited in nature and will not replace themselves. They can be exhausted by human activities. As they are limited, they are also called exhaustible resources. Coal, petroleum and natural gas are exhaustible fossil fuels, which cannot be prepared in the laboratory. It takes millions of years for dead organisms to get converted into these fuels.

Studies show that the known reserves of these fuels are fast depleting. Burning of these fuels is also a major cause for air pollution and, along with cutting down of trees, is contributing to global warming. The Petroleum Conservation Research Association (PCRA) of India has some tips for people on how to save petrol/ diesel while driving:

  • Drive vehicles at a constant and moderate speed.
  • While waiting or at a traffic junction, switch off the engine.
  • Ensure correct tyre pressure.
  • Ensure regular maintenance checks of the vehicle.

Tips for conserving energy at home and school:

  • Switch off lights and electrical appliances when not in use.
  • Turn off air conditioning when leaving the room.
  • Do not let the tap run while you brush your teeth or soap your hands.
  • Check all leaky taps.
  • Take shorter showers.
  • Buy rechargeable batteries and a charger for them.
  • Avoid plastic bags.
  • Recycle your newspapers.

Coal
During the carboniferous age, the earth had large amounts of plant life and dense forests in swampy and low-lying wetland areas. Plants and other life forms, after their death, drifted down to the bottom of the swamps, where they were compressed and decomposed to form peat. Coal was formed due to the compression of the peat at high temperature and pressure. As coal was formed from the remains of vegetation, it is called a fossil fuel. Carbonisation is the slow process of conversion of dead vegetation into coal.

Coal is primarily made up of carbon, also hydrogen, oxygen, nitrogen and some amounts of sulphur. Surface mining is used when coal is found close to the surface or hillsides. Underground mining is used to extract coal that is deep beneath the surface of the earth. Coal is processed in the industry to get useful products coke, coal tar and coal gas. Coke is an almost pure form of carbon that is used in the manufacture of steel and extraction of metals.

Coal tar is a black, thick mixture of almost 200 substances. It is used as a starting material for manufacturing synthetic dyes, explosives, perfumes, drugs and plastics, synthetic resins, paints and stains. Naphthalene balls, which are used to repel moths and other insects, are also obtained from coal tar. Bitumen, a petroleum product, is now used in place of coal tar for surfacing roads. Coal gas is obtained during the processing of coal to get coke. It is mainly used as a fuel in industries around coal processing plants.

Uses of coal:

  • Coal is the largest source of fuel used to generate electricity world-wide.
  • Coal is used in manufacturing industries for heat and power applications.
  • Coal is used to make steam for heating.
  • It is also used as coke in steel making.

Resources occurring naturally are called natural resources. These are of two types:

  1. Inexhaustible natural resources
  2. Exhaustible natural resources

Resources available in unlimited quantity and not likely to be exhausted by human activity are called inexhaustible natural resources.
Examples: Sunlight and air.

Resources available in limited quantity and likely to be exhausted by human activity are called exhaustible natural resources.
Examples: Forests, wildlife, minerals and coal.

Coal:

  • It is black in colour.
  • It is solid like a rock.
  • It was used in railway engines as fuel in the olden days.
  • It is used in thermal power production.
  • It is used in various industries.

Millions of years ago, when forests got buried, the dead plants got converted into coal due to the high pressure and temperature under the soil. This process of conversion of dead vegetation into coal is called carbonation. Coal is formed from the remains of vegetation, and hence, it is called fossil fuel.
Coal is processed in the industry to get different products like coke, coal tar, coal gas, etc.

Coke:

  • It is a porous and black substance.
  • It is a pure form of carbon.
  • It is used in the extraction of steel and many other metals.

Coal tar:

  • It is a black thick liquid with an unpleasant smell.
  • It is a mixture of 200 substances.
  • The products obtained from coal tar are used as starting materials for manufacturing substances like dyes, drugs, explosives and perfumes.

Coal gas:

  • Coal gas is obtained during the processing of coal to coke.
  • It is used as a fuel in many industries.

Petroleum
Petroleum, a natural resource formed from organisms living in the sea, is a dark and oily liquid mixture with a very unpleasant odour.
Petroleum and natural gas are formed from compressed organic matter. As petroleum and natural gas are lighter than water, the deposits of petroleum and natural gas occur above that of water. The first oil well in the world was drilled in Pennsylvania, USA. Oil in India is found in Assam, Gujarat and Mumbai High, and in the river basins of Godavari and Krishna. 

Petroleum is a mixture of various constituents like petroleum gas, petrol, diesel, lubricating oil, paraffin wax, etc., and the process of separating its many constituents is called refining. It is refined in a petroleum refinery. At the refinery, the crude oil mixture is 'fractionated' into different components by fractional distillation.
Light gases are the topmost fraction, followed by petrol and kerosene. Diesel is the heaviest. The other heavier fractions are not useful and are usually used to make asphalt to surface roads.

Constituents of petroleum and their uses:

  • LPG or petroleum gas is used as a fuel for home and industry.
  • Petrol is used as a motor fuel, aviation fuel and a solvent for dry cleaning.
  • Kerosene is used as a fuel for stoves and lamps and also in jet aircraft.
  • Diesel is used as a fuel for heavy motor vehicles and electric generators.
  • Lubricating oil is used for many lubricating purposes.
  • Paraffin wax is used in ointments, candles and Vaseline.
  • Bitumen is used in paints and also to surface roads.
  • Petrochemicals are used in the manufacture of detergents, polyester and nylon fibres, polythene and other man-made plastics.

Simple steps to reduce consumption of petrol/diesel:

  • Use public transport.
  • Combine many errands into one trip.
  • Car pooling to school and work.
  • Burning petroleum releases carbon dioxide into the air, which contributes to global warming. Oil spills at sea are devastating to the animal and plant life in and around the sea.

Natural Gases

Chapter Notes - Coal & Petroleum Class 8 Notes | EduRev

Natural gas is another fossil fuel, like coal and petroleum. It is a non-renewable fuel. Natural gas is used for waste treatment and incineration. Gases like butane, ethane and propane may be extracted from it and used as feedstock for products such as fertilisers and pharmaceutical products

Natural gas is one of the most useful, clean and safe energy sources. It is a colourless and odourless gas in its pure form, and is made up of many
gases, of which methane is the most prominent. The chemical formula for methane is CH4. When natural gas burns, it gives off a great deal of energy, and unlike other fossil fuels, leaves no ash. It causes very little air pollution, as methane burns almost completely.

It is one of the cleanest burning fuels and produces mostly heat, carbon dioxide and water vapour. Thus, it is said that it contributes to a cleaner and greener environment. Natural gas is odourless. To detect gas leaks, a harmless but pungent odorant that smells like rotten eggs is added to it, as a safety measure. It can be smelt in case of even a small leak.

Natural gas is measured in British Thermal Units (BTU). Uses of natural gas: For cooking. To run central heating and cooling systems, and cloth dryers. For electricity generation through the use of gas turbines and steam turbines. In the manufacture of fabrics, glass, steel, plastics, paint and other products.

Natural gas is compressed to a high pressure and stored in hard cylindrical or spherical containers, for distribution. It is then known as Compressed Natural Gas or CNG.
CNG is also distributed to homes and industries through pipes, For example, in India, such a network of pipelines exists in Vadodara in Gujarat and some parts of Delhi. CNG is now used as a fuel for transport vehicles - from light duty trucks, auto rickshaws and taxi cabs to delivery vans and heavy duty vehicles like buses.

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