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CBSE Important Questions

CBSE Guess > Papers > Important Questions > Class X > 2014 > Chemistry > Chemistry By Mrs. Kritika Bhola


Coal and Petroleum

When a fuel is burned , the energy is released mainly as heat which can be used for various purposes like cooking, heating , etc. Most of the fuels are either free carbon or carbon compounds. They are obtained from coal, petroleum and natural gas which are also called Fossil Fuels because they were formed by the decomposition of the remains of the pre-historic plants and animals buried under the earth long ago.

Formation of coal -  It is formed by the decomposition of large land plants and trees buried under the earth millions of years ago. Due to high temp. and pressure inside the earth, and in absence of air, wood was converted into coal.

Formation of petroleum -  It was formed by the decomposition of  the remains of extremely small plants and animals buried under the sea millions of years ago. It is a dark coloured, viscous and foul smelling crude oil which is a mixture of  several solid, liquid and gaseous hydrocarbons mixed with water , salt an dearth particles.

  • The fuels such as coal and petroleum have some nitrogen and sulphur in them . So, when they burn they lead to oxides of nitrogen and sulphur which are major pollutants of air.

    Burning of substances with or without flame ----
    A flame is a region where combustion of gaseous substances takes place. So, a flame is produced only when gaseous substances burn.
  • All gaseous substances burn with a flame but only those solid and liquid fuels which vaporize on heating burn with a flame.
  • Two types of flames  -  Blue ;  Yellow
  • Colour of flame depends upon the proportion of oxygen available for burning of fuel.
  • Blue  Flame  -  When the oxygen supply is sufficient . It does not produce much  light – Non-luminous .eg. gas stove.

  • Yellow  Flame  -  Oxygen supply insufficient . Yellow color is due to the glow of hot, unburnt carbon particles produced due to incomplete combustion of fuel .It produces light – Luminous. Eg. candle
  • Solid and liquid fuels which do not vaporise on heating , burn without producing a charcoal and coal.

Submitted By Mrs. Kritika Bhola
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