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SAI International School
Subject - Chemistry
Class - VIII
Topic – Combustion and Flame
Sub-Topic-Conditions required for combustion

LESSON NOTES

Conditions necessary for combustion

Three conditions are necessary for the process of combustion to take place. These are:

1. Presence of a combustible substance. (presence of a fuel)
2. Presence of supporter of combustion. (air or oxygen)
3. Heating the combustible substance to its ignition temperature.

Let us discuss in detail about these conditions.

1. Combustible substance
The presence of a combustible substance is necessary for combustion to take place. For
example, if we have to start a fire we use combustible substances or fuel like cloth, paper,
wood, etc.
2. Supporter of combustion
The most common supporter of combustion which we have around us is air or oxygen. We
can say that air is necessary for combustion. In class 6 you have read that oxygen or air is
necessary for burning.
3. Ignition temperature
The lowest temperature at which a substance catches fire and starts burning is called its
ignition temperature.
Before a combustible substance can catch fire and burn, it must be heated to a certain
minimum temperature by supplying heat from outside. It will not catch fire as long as its
temperature is lower than its ignition temperature.
For example, the ignition temperature of paper is 233 C. So a paper should be heated to
0
0
233 C to start burning. To burn a paper we generally use a matchstick which supplies heat
to raise the temperature of the paper to its ignition temperature.
Similarly, a match stick does not catch fire and burn on its own at room temperature
because the ignition temperature of the match stick is much higher than the room
temperature. It can be lighted by rubbing it on the rough surface provided on the side of the
matchbox.
*Ignition temperature of different substances is different.
i. Some substances have a low ignition temperature.
For example paper, dry grass, etc.
Those substances which have very low ignition temperature and can easily catch
fire are called inflammable substances.
For example LPG, Kerosene, etc.

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