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Question

(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.


Solution

(a) When carbon is burned in air, it forms carbon dioxide gas and releases a large amount of heat and some light: 
      $$C + O_{2} \rightarrow CO_{2} + Heat + Light$$
(b) Coal and petroleum are called fossil fuels because they were formed by the decomposition of the remains of the prehistoric plants and animals (fossils) buried under the earth long, long, ago.
(c) Coal was formed by the decomposition of large plants and trees buried under the earth millions of years ago. It is believed that millions of years ago, due to earthquakes and volcanoes, etc., the forests were buried under the surface of the earth and got covered with sand, clay, and water. Due to high temperature and high pressure inside the earth and in the absence of air, wood was converted into coal.
(d) Petroleum oil was formed by the decomposition of the remains of extremely small plants and animals buried under the sea millions of years ago. It is believed that millions of years ago, the microscopic plants and animals which lived in the sea have died. Their bodies sank to the bottom of the sea and were soon covered with mud and sand. The chemical effects of pressure, heat, and bacteria, converted the remains of microscopic plants and animals into petroleum oil and natural gas just as they converted forest trees into coal. This conversion took place in the absence of oxygen or air. The petroleum thus formed got trapped between two layers of impervious rocks (non-porous rock) forming an oil trap.
(e) Fossil fuel other than coal and petroleum is Natural gas.

Science

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