NCERT Book Class 8 Science Chapter 4 Combustion and Flame

COMBUSTION AND FLAME

W
e use different kinds of fuel for
various purposes at home, in
industry and for running
automobiles. Can you name a few fuels
used in our homes? Name a few fuels
used in trade and industry. What fuels
are used for running automobiles? Your
list will contain fuels like cowdung,
wood, coal, charcoal, petrol, diesel,
compressed natural gas (CNG), etc.
You are familiar with the burning of a
candle. What is the difference between the
burning of a candle and the burning of a
fuel like coal? May be you were able to
guess right: candle burns with a flame
whereas coal does not. Similarly, you will
find many other materials burning
Fig. 4.1 : Burning of magnesium
without a flame. Let us study the chemical
process of burning and the types of flame A chemical process in which a
produced during this process. substance reacts with oxygen to give
off heat is called combustion. The
4.1 What is Combustion? substance that undergoes combustion
Recall the activity of burning of is said to be combustible. It is also called
magnesium ribbon per for med in a fuel. The fuel may be solid, liquid or
Class VII. We learnt that magnesium gas. Sometimes, light is also given off
burns to form magnesium oxide and during combustion, either as a flame or
produces heat and light (Fig. 4.1). as a glow.
We can perform a similar activity with In the reactions mentioned
a piece of charcoal. Hold the piece with above magnesium and charcoal are
a pair of tongs and bring it near the combustible substances.
flame of a candle or a Bunsen burner.
What do you observe?
We find that charcoal burns in air.
We know that coal, too, burns in air We were told that
food is a fuel for
producing carbon dioxide, heat and
our body.
light.