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Science: Class 8 — Chapter 3: Coal and Petroleum

3.0 Introduction to Resources
3.0.1 Types of Resources
  • Natural Resources: Materials found in nature (e.g., air, water, soil, minerals, sunlight).
  • Man-made Resources: Materials produced by human efforts.
  • Inexhaustible Natural Resources: Present in unlimited quantity, not likely to be exhausted by human activities (e.g., sunlight, air).
  • Exhaustible Natural Resources: Limited amount in nature, can be exhausted by human activities (e.g., forests, wildlife, minerals, coal, petroleum, natural gas).
3.0.2 Understanding Exhaustible Resources
  • Activity 3.2: A group activity demonstrating the limited availability and consumption patterns of exhaustible resources across generations.
  • Fossil Fuels: Exhaustible natural resources like coal, petroleum, and natural gas, formed from the dead remains of living organisms (fossils).
3.1 Coal
3.1.1 Properties and Uses of Coal
  • Appearance: Hard as stone, black in colour (Fig. 3.1).
  • Uses: Fuel for cooking food, in railway engines to produce steam, in thermal power plants to produce electricity, and as fuel in various industries.
3.1.2 Story of Coal (Formation)
  • Origin: Formed about 300 million years ago from dense forests in low-lying wetland areas.
  • Process: Forests got buried under soil due to natural processes like flooding, compressed, and temperature rose as they sank deeper.
  • Conversion: Under high pressure and high temperature, dead plants slowly converted to coal.
  • Carbonisation: The slow process of conversion of dead vegetation into coal, as coal contains mainly carbon.
  • Fossil Fuel: Coal is also called a fossil fuel because it was formed from the remains of vegetation.
3.1.3 Products of Coal
  • Burning Coal: When heated in air, coal burns and produces mainly carbon dioxide gas.
  • Industrial Processing: Coal is processed in industry to get useful products.
  • Coke: A tough, porous, black substance, an almost pure form of carbon. Used in the manufacture of steel and extraction of many metals.
  • Coal Tar: A black, thick liquid with an unpleasant smell (Fig. 3.3). It is a mixture of about 200 substances.
  • Uses of Coal Tar Products: Starting materials for manufacturing synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, etc.
  • Naphthalene Balls: Obtained from coal tar, used to repel moths and other insects.
  • Bitumen: A petroleum product, now used in place of coal tar for metalling roads.
  • Coal Gas: Obtained during the processing of coal to get coke.
  • Historical Use of Coal Gas: First used for street lighting in London (1810) and New York (around 1820).
  • Modern Use of Coal Gas: Used as a source of heat rather than light, and as a fuel in many industries near coal processing plants.
3.2 Petroleum
3.2.1 Introduction and Formation of Petroleum
  • Common Fuels: Petrol (light automobiles), diesel (heavy motor vehicles). Both obtained from petroleum.
  • Etymology: The word petroleum is derived from 'petra' (rock) and 'oleum' (oil), as it is mined from between rocks under Earth (Fig. 3.4).
  • Formation: Formed from organisms living in the sea. Their bodies settled at the bottom and were covered with layers of sand and clay.
  • Conditions for Formation: Over millions of years, absence of air, high temperature, and high pressure transformed dead organisms into petroleum and natural gas.
  • Layering: Petroleum oil and gas layers are above water because oil and gas are lighter and do not mix with water.
3.2.2 Petroleum Deposits and Discovery
  • World's First Oil Well: Drilled in Pennsylvania, USA, in 1859.
  • Oil in India: Struck at Makum in Assam in 1867. Found in Assam, Gujarat, Mumbai High, and river basins of Godavari and Krishna.
3.2.3 Refining of Petroleum
  • Crude Petroleum: A dark oily liquid with an unpleasant odour, a mixture of various constituents.
  • Refining: The process of separating various constituents or fractions of petroleum.
  • Petroleum Refinery: Where refining is carried out (Fig. 3.5).
  • Petroleum Constituents and Uses (Table 3.1):
  • Petroleum Gas (LPG): Fuel for home and industry.
  • Petrol: Motor fuel, aviation fuel, solvent for dry cleaning.
  • Kerosene: Fuel for stoves, lamps, and jet aircrafts.
  • Diesel: Fuel for heavy motor vehicles, electric generators.
  • Lubricating oil: Used for lubrication.
  • Paraffin wax: Used in ointments, candles, vaseline, etc.
  • Bitumen: Used in paints, road surfacing.
  • Petrochemicals: Useful substances obtained from petroleum and natural gas.
  • Uses of Petrochemicals: Manufacturing detergents, fibres (polyester, nylon, acrylic), polythene, and other man-made plastics.
  • Hydrogen Gas: Obtained from natural gas, used in the production of fertilisers (urea).
  • Black Gold: Petroleum is called 'black gold' due to its great commercial importance.
3.3 Natural Gas
3.3.1 Characteristics and Uses of Natural Gas
  • Importance: A very important fossil fuel, easy to transport through pipes.
  • Storage: Stored under high pressure as Compressed Natural Gas (CNG).
  • Uses of CNG: Power generation, transport fuel (less polluting, cleaner fuel).
  • Domestic/Industrial Use: Can be used directly for burning in homes and factories through pipeline networks (e.g., Vadodara, parts of Delhi).
  • Chemical/Fertiliser Production: Used as a starting material for manufacturing various chemicals and fertilisers.
3.3.2 Natural Gas Reserves in India
  • Reserves: India has vast reserves of natural gas.
  • Locations: Found in Tripura, Rajasthan, Maharashtra, and the Krishna Godavari delta.
  • Laboratory Formation: Coal, petroleum, and natural gas cannot be prepared in the laboratory as their formation is a very slow process requiring specific conditions.
3.4 Some Natural Resources are Limited
3.4.1 Exhaustible Nature of Fossil Fuels
  • Formation Time vs. Availability: Took millions of years for fossil fuels to form, but known reserves will last only a few hundred years.
  • Environmental Concerns: Burning these fuels is a major cause of air pollution and is linked to global warming.
  • Judicious Use: Necessary to use these fuels only when absolutely necessary for a better environment, smaller risk of global warming, and longer availability.
3.4.2 Petroleum Conservation Tips (PCRA)
  • PCRA Advice: The Petroleum Conservation Research Association (PCRA) advises people on saving petrol/diesel while driving.
  • Tips:
  • Drive at a constant and moderate speed as far as possible.
  • Switch off the engine at traffic lights or when waiting.
  • Ensure correct tyre pressure.
  • Ensure regular maintenance of the vehicle.
What You Have Learnt