Combustion and flame · दहन और ज्वाला
A free Chemistry lesson for Class 8 children.
Combustion is a chemical process in which a substance reacts with oxygen to give heat, and often light.
Three things are needed: a fuel, air, and heat to reach the ignition temperature. Remove any one and the fire goes out.
A fire extinguisher works by cutting off air, cooling the fuel, or both. Carbon dioxide extinguishers are used for electrical fires.
A candle flame has three zones. The outer blue zone is the hottest, where combustion is complete.
The middle yellow zone is luminous. The dark inner zone has unburnt wax vapour and is the least hot.
A good fuel is cheap, easily available, burns easily without smoke, and gives a lot of heat. Its calorific value is measured in kilojoules per kilogram.
Burning fuels releases carbon dioxide, which warms the Earth, and sulphur oxides, which cause acid rain.