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Combustion - Lesson Summary

The chemical process in which a substance reacts with oxygen to give off heat is called combustion.

Substancec which undergoes combustion are called a combustible substances or a fuels.
Example: LPG, kerosene, petrol...etc
Substances which do not burn in air and oxygen are called non-combustible substances.
Example: Iron, glass, water...etc

Types of combustion:
The type of combustion differs depending on the type of fuel.  Based on nature and intensity combustions are classified into three types. They are:
Rapid combustion
Spontaneous combustion

Rapid combustion:
The combustion in which large amount heat produced within a very short time is called rapid combustion.
Example: Liquefied Petroleum Gas (LPG) burns very quickly producing a lot of heat. 

Spontaneous combustion:
The combustion which produced without application external source of heat is called spontaneous combustion.
When white phosphorous is left out in the open at room temperature for some time, it burns all by itself. Forest fires and fires in coal mines are because of spontaneous combustion. 

The combustion which is accompanied by the release of heat, light, sound and large amount of heat is called explosion.
The burning of crackers produces a large amount of heat, light and sound because of chemical reaction. 

Ignition temperature:
Temperature is an important condition for combustion to occur. The lowest temperature at which a substance catches fire is called its ignition temperature. 
Kerosene is a fuel that has a low ignition temperature.

Substance with low ignition temperature is highly inflammable and will catches fire very quickly
Example: Some inflammable substances are petrol, LPG, ether and alcohol.

Important requirements for combustion:
Air, heat and fuel are needed for a fire to be created.
A substance will not catch fire if it does not reach its ignition temperature.
Combustible substances need availability of oxygen as well as the right amount of heat in order to combust.

Extinguishion of fire:
Fire can be easily stopped by stopping the supply of either air or heat. 
Water is not a good extinguisher for electrical fires.  If electrical wiring is on fire, pouring water on it will conduct the electricity through the water and may cause the person dousing the fire to be electrocuted.

As water is heavier than petrol, it is not useful for extinguishing oil or petrol fires.
For electrical and oil fires, it is best to use carbon dioxide as an extinguisher. Carbon dioxide is heavier than oxygen, so it covers the flame like a blanket, cutting off contact between the fuel and oxygen. Powder of sodium or potassium bicarbonate can also be used to get carbon dioxide.

The first automatic fire extinguisher was patented in England by a celebrated chemist called French C. Hopffer. 
The modern fire extinguisher was invented by British Captain George William Manby.


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