6. Combustion And Flame Science class 8 in English Medium ncert book solutions 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.