(a) What happens when carbon burns in air? Write the chemical equation of the reaction which takes place.
(b) Why are coal and petroleum called fossil fuels?
(c) Explain how coal was formed in the earth.
(d) Describe how petroleum was formed in the earth.
(e) Name a fossil fuel other than coal and petroleum.

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(a) When carbon is burned in air, carbon dioxide is evolved along with a large amount of heat and light energy.

The chemical equation of the above reaction is as follows:


(b) Coal and petroleum are called fossil fuels because they are produced through the decomposition of the pre-historic organisms (plants and animals) buried deep in the soil since millions of years ago.

(c) Coal evolved in the Earth millions of years ago by the decomposition of trees and plants that got buried deep into the soil. Natural phenomena like volcanoes and earthquakes caused the forests to get buried deep under the surface of the Earth. The extreme temperature and pressure inside the soil converted the wood into coal in the absence of air.

(d) Petroleum evolved, millions of years ago, through the decomposition of the microscopic remains of the plants and animals buried deep under the sea. When the marine plants and animals died, millions of years back, their bodies sank to the bottom of the sea, thereby getting buried into the sand and mud. The high pressure, heat and bacteria caused the chemical reactions in the absence of air and converted the microscopic remains into petroleum. This is the reason why petroleum is found trapped between two layers of non-porous rocks.

(e) Other than coal and petroleum, natural gas is a fossil fuel.

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