Page 110 - ICSE Chemistry 8

In reactants In products
Number of Fe atoms: 4 4

Number of O atoms: 6 6
The chemical equa on, 4Fe + 3O  2Fe O , now contains an equal number of atoms in
2
2
3
reactants and products. Therefore, we can say that it is a balanced equa on.
Example 4: Magnesium and oxygen react to form magnesium oxide.

Magnesium + Oxygen  Magnesium oxide

Mg + O  MgO
2
In reactants In products
Number of Mg atoms: 1 1

Number of O atoms: 2 1
The number of magnesium atoms is equal on both the sides. However, there are two oxygen
atoms on the le side and one oxygen atom on the right side. In order to have an equal
number of magnesium and oxygen atoms on both the sides, we mul ply Mg by 2 on the le -
hand side and we mul ply MgO by 2 on the right-hand side.

By doing so, the equa on changes in the given form.

2Mg + O  2MgO
2
In reactants In products

Number of Mg atoms: 2 2
Number of O atoms: 2 2

The chemical equa on, 2Mg + O  2MgO, now contains an equal number of various
2
atoms in reactants and products. Therefore, we can say that it is a balanced equa on.

Example 5: Hydrogen and chlorine react to form hydrogen chloride.
Hydrogen + Chlorine  Hydrogen chloride

H + Cl  HCl
2
2
In reactants In products
Number of H atoms: 2 1

Number of Cl atoms: 2 1

The number of hydrogen atoms and chlorine atoms are not equal. There are two hydrogen
atoms on the le -hand side and one hydrogen atom on the right-hand side. Also, there are two
chlorine atoms on the le -hand side and one chlorine atom on the right-hand side. In order to
have an equal number of hydrogen and chlorine atoms on both the sides, we mul ply HCl by
2 on the right-hand side. By doing so, the equa on changes in the given form.
H + Cl  2HCl
2
2

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