Class 8 Science Notes Chapter 5 (Coal and Petroleum) – Science Book

Below are the structured notes for Chapter 5 – Coal and Petroleum from NCERT Class 8 Science, optimized for government exam preparation.

Chapter 5: Coal and Petroleum

1. Introduction: Natural Resources

• Definition: Resources obtained from nature are called Natural Resources.
• Classification based on Availability:
  • Inexhaustible Natural Resources: Present in unlimited quantity in nature and are not likely to be exhausted by human activities.
    • Examples: Sunlight, Air.
  • Exhaustible Natural Resources: Present in limited quantity in nature and can be exhausted by human activities over time.
    • Examples: Forests, Wildlife, Minerals, Coal, Petroleum, Natural Gas.
• Focus of the Chapter: This chapter deals with exhaustible natural resources like Coal, Petroleum, and Natural Gas, which are formed from the dead remains of living organisms (fossils). Hence, they are also known as Fossil Fuels.

2. Fossil Fuels

• Definition: Fuels formed over millions of years from the buried dead remains of ancient organisms (plants and animals) under high temperature and pressure.
• Key Examples: Coal, Petroleum, Natural Gas.
• Nature: They are exhaustible resources.

3. Coal

• Appearance: Hard as stone, black in colour.
• Use: Primarily used as fuel (cooking, thermal power plants, industries), earlier used in railway engines (steam).
• Formation (Carbonisation):
  • About 300 million years ago, 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.
  • Temperature and pressure increased as they sank deeper.
  • Under high pressure and high temperature, dead plants got slowly converted to coal.
  • This slow process of conversion of dead vegetation into coal is called Carbonisation.
  • Since coal was formed from the remains of vegetation, it is considered a fossil fuel.
• Processing of Coal: When coal is heated strongly in the absence of air (destructive distillation), several useful products are obtained.
  • Coke:
    • Properties: Tough, porous, black substance. Almost pure form of carbon.
    • Uses: Manufacture of steel, extraction of many metals.
  • Coal Tar:
    • Properties: Black, thick liquid with an unpleasant smell. It is a mixture of about 200 substances.
    • Uses: Starting materials for manufacturing various substances like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, etc.
    • Note: Naphthalene balls (used to repel moths/insects) are obtained from coal tar. Bitumen (a petroleum product) is now often used instead of coal tar for metalling roads.
  • Coal Gas:
    • Properties: Gaseous fuel obtained during the processing of coal to get coke.
    • Uses: Used as fuel in many industries situated near coal processing plants. (Historically used for street lighting).

4. Petroleum

• Appearance: Dark, oily liquid with an unpleasant odour.

• Name Origin: Petra (rock) + Oleum (oil) = Petroleum (oil from rock).

• Formation:

  • Formed from organisms living in the sea.
  • When 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.

• Occurrence:

  • Found trapped in porous rocks under impervious rock layers.
  • Petroleum oil and gas layers are usually found above water layer (since oil and gas are lighter than water).
  • Extracted by drilling oil wells.

• Refining of Petroleum:

  • Petroleum is a mixture of various constituents like petroleum gas, petrol, diesel, lubricating oil, paraffin wax, etc.
  • The process of separating the various constituents/fractions of petroleum is known as Refining.
  • This is carried out in a Petroleum Refinery using the technique of Fractional Distillation (separation based on different boiling points).

• Constituents of Petroleum and their Uses:

  Constituent	Uses
  Petroleum Gas (in liquid form - LPG)	Fuel for home and industry
  Petrol (Gasoline)	Motor fuel, aviation fuel, solvent for dry cleaning
  Kerosene	Fuel for stoves, lamps, and jet aircraft
  Diesel	Fuel for heavy motor vehicles, electric generators
  Lubricating Oil	Lubrication
  Paraffin Wax	Ointments, candles, vaseline, wax paper
  Bitumen	Paints, road surfacing (metalling)

• Petrochemicals:

  • Definition: Many useful substances obtained from petroleum and natural gas are termed Petrochemicals.
  • Uses: Manufacture of detergents, synthetic fibres (polyester, nylon, acrylic), polythene and other man-made plastics.
  • Hydrogen gas obtained from natural gas is used in the production of fertilizers (e.g., urea).

• "Black Gold": Due to its great commercial importance and wide range of uses, petroleum is also called 'Black Gold'.

5. Natural Gas

• Importance: A very important fossil fuel.
• Transport: Easy to transport through pipes.
• Storage: Stored under high pressure as Compressed Natural Gas (CNG).
• Uses of CNG:
  • Power generation.
  • Fuel for transport vehicles (less polluting, cleaner fuel compared to petrol/diesel).
  • Can be supplied directly for burning in homes and factories through pipes.
• Other Uses: Starting material for the manufacture of a number of chemicals and fertilizers.
• Occurrence: Often found along with petroleum deposits in oil wells. Also found in standalone gas fields.
• Major Reserves in India: Tripura, Rajasthan, Maharashtra, and in the Krishna Godavari delta.
• Advantage of CNG: The great advantage is that it is a cleaner fuel, causing less pollution when burnt compared to petrol or diesel.

6. Limitations of Fossil Fuels

• Exhaustible:
  • They are finite resources.
  • It took millions of years for them to form.
  • Current consumption rates are high, meaning known reserves will last only for a limited period (e.g., a few hundred years for coal, much less for petroleum at current rates).
• Environmental Pollution:
  • Burning fossil fuels is a major source of air pollution.
  • They release unburnt carbon particles (causing respiratory diseases), carbon monoxide (poisonous gas), carbon dioxide, sulphur dioxide, and nitrogen oxides.
  • Acid Rain: Oxides of sulphur and nitrogen dissolve in rainwater to form acids, leading to acid rain, which is harmful to crops, buildings, and soil.
  • Global Warming: Increased concentration of carbon dioxide (CO2) in the atmosphere traps heat (greenhouse effect), leading to a gradual increase in the Earth's average temperature, known as global warming. This can cause melting of glaciers, rise in sea levels, and changes in climate patterns.

7. Conservation of Fossil Fuels

• Need: Essential because they are exhaustible and their use causes environmental damage.
• Strategies:
  • Use fossil fuels only when absolutely necessary.
  • Promote the use of alternative sources of energy like solar energy, wind energy, hydro energy, geothermal energy, etc. (though these are not the focus of this chapter, awareness is important).
  • Improve efficiency of machines using these fuels.
  • Practice energy conservation in daily life.
• PCRA (Petroleum Conservation Research Association) Advice (India):
  • Drive vehicles at a constant and moderate speed.
  • Switch off the engine at traffic lights or places where you have to wait.
  • Ensure correct tyre pressure.
  • Ensure regular maintenance of the vehicle.

Key Terms to Remember:

• Natural Resources: Inexhaustible, Exhaustible
• Fossil Fuels: Coal, Petroleum, Natural Gas
• Carbonisation: Formation of coal
• Destructive Distillation: Processing coal in absence of air
• Coke, Coal Tar, Coal Gas: Products of coal processing
• Petroleum Refining: Separating petroleum constituents
• Fractional Distillation: Technique used in refining
• LPG: Liquefied Petroleum Gas
• CNG: Compressed Natural Gas
• Petrochemicals: Useful chemicals from petroleum/natural gas
• Acid Rain: Rain containing dissolved acidic oxides
• Global Warming: Increase in Earth's temperature due to greenhouse gases like CO2
• PCRA: Petroleum Conservation Research Association

This comprehensive summary covers the key concepts, processes, products, uses, and consequences related to coal and petroleum as detailed in the NCERT Class 8 textbook, keeping in mind the requirements for government exam preparation. Focus on definitions, processes (like carbonisation, refining), products and their specific uses, and the environmental impact/conservation aspects.