Class 8 Science
Natural Resources: Resources which from nature are called natural resources. Examples: coal, petroleum, air, water, soil, etc.
Inexhaustible Natural Resources: Some natural resources are available in huge quantity and cannot be finished by human activities. Such resources are called inexhaustible natural resources, e.g. air, water, sunlight, etc.
Exhaustible Natural Resources: Some natural resources are available in limited quantity and can be finished by human activities. Such resources are called exhaustible natural resources, e.g. coal, petroleum, minerals, etc.
Fossil Fuels: Coal and petroleum were formed from dead remains of plants and animals which got buried millions of years ago. Due to this, coal and petroleum are called fossil fuels.
Fossil: Dead remains of organisms which are more than 10,000 years old are called fossils.
Coal is a fossil fuel. It is hard as stone, black in colour and is mainly composed of carbon.
Formation of Coal:
- There were dense forests in low lying areas on earth; about 300 million years ago.
- Those forests got buried under the soil due to natural processes.
- More layers of soil were deposited on these buried forests in due course of time.
- Those plants were converted into coal due to intense pressure and heat inside the earth.
Carbonisation: The process of conversion of vegetation into coal is called carbonization. The buried plants underwent carbonization and changed into coal.
Uses of Coal
Coal burns in air to produce heat and carbon dioxide. Coal is used as fuel because it provides high amount of heat.
C + O2 → CO2
- Coal was used as fuel in steam engines.
- Most of the thermal power plants still use coal as fuel.
- Coal is still being used as kitchen fuel in some households, dhabas and restaurants.
- Many useful products; like coke, coal tar and coal gas; are made by processing coal.
Coke: Coke is almost pure form of carbon, is tough, porous and black. Coke is used in manufacture of steel and extraction of many metals.
Coal Tar: It is a black thick liquid with an unpleasant smell. Coal tar is a mixture of about 200 substances. It is used as raw material for making various items; like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, naphthalene balls, etc. It is used for making the surface of roads. Bitumen (a petroleum product) has almost replaced coal tar for making road surface.
Coal Gas: Coal gas is produced during processing of coke from coal. Coal gas is used as fuel in many industries which are situated near coal mines.