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NCERT Solutions for Class 8th Science

 

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Chapter 6. Combustion And Flame

Chapter Review

 

 

 

Chapter Review:

  • The chemical process in which a substance reacts with oxygen and gives heat is called combustion. 
  • The substance that undergoes combustion is said to be combustible. It is also called a fuel.

  • The lowest temperature at which a substance catches fire is called its ignition temperature. 

  • The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its calorific value. Its unit is kilojoules per kg (kj/kg) 

  • The substances which have very low ignition temperature and can
    easily catch fire with a flame are called inflammable substances. Examples of inflammable substances are petrol, alcohol, Liquified Petroleum Gas (LPG), etc.

  • There are three different zones of a flame - dark zone, luminous zone and non-luminous zone.

  • Phosphorus which burns in air at room temperature.

  • The type of combustion in which a material suddenly bursts into flames, without the application of any apparent cause is called spontaneous combustion.

  • A large amount of gas formed in the reaction is liberated. Such a reaction is called explosion.

  • The sources of heat energy for domestic and industrial purposes are mainly wood, charcoal, petrol, kerosene, etc. These substances are
    called fuels.

  • Combustion of most fuels releases carbon dioxide in the environment.
    Increased concentration of carbon dioxide in the air is believed to cause global warming.

  • Oxides of sulphur and nitrogen dissolve in rain water and form acids. Such rain is called acid rain.

  • Incomplete combustion of a fuel gives poisonous carbon monoxide gas.

  • An ideal fuel is cheap, readily available, readily combustible and easy to transport. It has high calorific value. It does not produce gases or
    residues pollute the environment.
    

 

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