Introduction The blacksmith burns coal to get hot iron which can be beaten to desired shape. A variety of fuels is used in daily life such as coal, petrol, charcoal, LPG, etc. Do you know which chemical process is taking place during the burning of these fuels?
It is combustion. In this lesson you will learn about combustion of fuels. objectives at the end of this lesson you will be able to explain combustion and its types define ignition temperature explain the necessary conditions for combustion describe fire extinguishers list types of combustion Rowan is performing a simple activity he is burning a magnesium wire on a flame notice carefully Heat and light is also produced along with magnesium oxide.
Now look at the burning of coal. This burns in air producing carbon dioxide, heat and light. In both the example, the substances are reacting with the oxygen of the air to produce heat and light.
This process is called combustion. There are two types of substances. Some substances catch fire and burns.
While the other group does not catch fire. As you can see, the boy is bringing a lighted matchstick close to the paper and glass. Paper catches fire, and so it is called combustible substance.
The glass does not burn, and such substances which cannot burn in air or oxygen are incombustible substances. Let us discuss the conditions necessary for burning. Light a candle and cover it with glass tumbler. You will see that candle stops burning after a while.
This implies that candle burns freely in the presence of air. Therefore, air is necessary for combustion. We just saw that a paper burns when lighted with a matchstick.
Now bring the matchstick close to the piece of wood. The piece of wood does not catch fire. One lighted matchstick is not able to burn the piece of wood, but a piece of paper burnt quickly. This is because a piece of wood has not reached its ignition temperature. Ignition temperature is the lowest temperature at which the substance catches fire.
Your mother would have told to keep burning matchstick or a lighter away from LPG gas stove in the kitchen. This is because LPG catches fire very easily. Similarly, you must have seen no smoking sign board at the petrol pumps. It is because petrol also catches fire very easily and therefore it is advisable not to smoke at the petrol pumps.
Substances like LPG and petrol are inflammable because they have low ignition temperature due to which they readily catch fire. Now we will see how the fire can be put off. Fire needs oxygen, heat and fuel to exist. However, it can be extinguished by removing any one of them. You must have seen fireman throwing water on the fire and the fire gets extinguished.
Water brings the temperature of the combustible material below its ignition temperature and cuts off the supply of air. But water is not a good extinguisher for electrical or oil fires. For electrical and oil fires, it is best to use carbon dioxide as an extinguisher. Carbon dioxide being heavier than oxygen covers the fire like a blanket due to which contact between the fuel and oxygen gets cut off. Let us now look at types of combustion.
You can see a lady igniting LPG in a kitchen to make food. LPG burns quickly producing a lot of heat. This type of combustion is called rapid combustion. When white phosphorus is left in the open for some time, it catches fire. This type of combustion is called spontaneous combustion.
Other example of spontaneous combustion is the forest fire and fires in coal mines. You must have used fireworks during festival days. what happens when the cracker burns the burning of a cracker produces a large amount of heat light and sound This type of combustion is called explosion.
Summary Let us summarize what we have learned. The substances which burn in air are called combustible. Oxygen in air is essential for combustion.
Ignition temperature is the lowest temperature at which a combustible substance catches fire. There are various types of combustions such as rapid combustion, spontaneous combustion, explosion, etc.