Page 109 - ICSE Chemistry 8

In reactants In products
Number of C atoms: 1 1
Number of H atoms: 4 2
Number of O atoms: 2 3

The number of carbon atoms are equal on both the sides but the number of hydrogen and
oxygen atoms are not equal. There are 4 hydrogen atoms on the le -hand side but only 2
hydrogen atoms on the right-hand side. In order to have 4 hydrogen atoms on the right-hand
side, we have to mul ply H O by 2.
2
CH + O CO + 2H O
2
2
4
2
Now there are 2 oxygen atoms on the le -hand side and 4 oxygen atoms on the right-hand
side. In order to have 4 oxygen atoms on the le -hand side, we have to mul ply O by 2. By
2
doing so, the equa on changes to the following.
CH + 2O CO 2 + 2H O
4
2
2
Again count the number of atoms on both the sides.
In reactants In products

Number of C atoms: 1 1

Number of H atoms: 4 4
Number of O atoms: 4 4

The chemical equa on, CH + 2O CO + 2H O, now contains an equal number of atoms
4
2
2
2
in the reactants and products. Hence, it is a balanced equa on.
Example 3: The reac on between iron and oxygen to form iron(III) oxide.
Write the word equa on.

Iron + Oxygen  Iron(III) oxide

Fe + O  Fe O 3
2
2
In reactants In products

Number of Fe atoms: 1 2
Number of O atoms: 2 3

The number of iron atoms and oxygen atoms are not equal. There is one iron atom on the
le -hand side and two iron atoms on the right-hand side. Also, there are two oxygen atoms on
the le -hand side and three oxygen atoms on the right-hand side. In order to have an equal
number of iron and oxygen atoms on both the sides, we mul ply Fe by 4 and O by 3 on the
2
le -hand side and we mul ply Fe O by 2 on the right-hand side.
3
2
By doing so, the equa on changes in the given form.

4Fe + 3O  2Fe O 3
2
2

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