Lecture 1: CLASS VIII: SCIENCE: CHAPTER 5: CLASSIFICATION OF NATURAL RESOURCES

 Natural Resources and Coal

Classification of Natural Resources:

Natural resources are materials provided by nature that are useful to humans. They are broadly classified into two categories:

1. Inexhaustible Natural Resources:

   • These are available in unlimited quantity and cannot be depleted by human use.

   • Examples: Sunlight, Air.

2. Exhaustible Natural Resources:

   • These are limited in amount and can be exhausted due to overuse by humans.

   • Examples: Coal, Petroleum, Natural Gas, Forests, Minerals, Wildlife.

An activity analogy is given where eatables in a container represent exhaustible resources. Different groups may consume these differently. Some earlier generations may have used too much (being greedy), while others may have been thoughtful and left some for future generations. This introduces the idea of sustainable use of resources.

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Fossil Fuels

Exhaustible natural resources like coal, petroleum, and natural gas are called fossil fuels because they are formed from the dead remains of living organisms over millions of years.

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Coal – A Fossil Fuel

• Appearance: Hard, black, stone-like substance.

• Uses:

  • Fuel for cooking (in some places)

  • Earlier used in steam engines of trains

  • Important in thermal power plants for electricity generation

  • Fuel in various industries

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Formation of Coal (Carbonisation):

• About 300 million years ago, dense forests in wetland areas were buried due to natural events like flooding.

• Over time, these were compressed under layers of soil.

• With increased pressure and temperature, the dead plant matter slowly turned into coal.

• This slow chemical change is called carbonisation.

• Since coal comes from plant remains, it is classified as a fossil fuel.

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By-products of Coal and Their Uses:

1. Coke:

   • Tough, porous, black substance

   • Almost pure carbon

   • Used in steel manufacturing and metal extraction

2. Coal Tar:

   • Thick, black liquid with an unpleasant smell

   • Contains over 200 different substances

   • Used for making:

     • Synthetic dyes

     • Drugs

     • Explosives

     • Perfumes

     • Plastics

     • Paints

     • Photographic and roofing materials

     • Naphthalene balls (used to repel insects)

   • Note: Bitumen (a petroleum product) has replaced coal tar for road construction in modern times.

3. Coal Gas:

   • Obtained when coal is processed to make coke

   • Used as a fuel in nearby industries

   • Historically used for street lighting (London: 1810, New York: 1820)

   • Now used mainly as a heat source

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Conclusion:

Coal is a vital fossil fuel that has powered industries and households for centuries. However, being an exhaustible resource, it must be used judiciously. Understanding its origin, uses, and by-products helps us make better decisions about its consumption and environmental impact.