Page 29 - Chemistry ICSE Class IX

The Language of Chemistry 17
Balancing of Chemical Equations

The method by which the number of atoms of each element on both the sides
of the arrow (o) in a chemical reaction are made equal, is called balancing
of chemical equation.

Why is it necessary to balance a chemical equation
In a balanced chemical equation, the number of atoms of each element on
both the sides should be equal. This is because no matter is lost or gained ĐŚĞŵŝĐĂů ĞƋƵĂƟŽŶ ŵƵƐƚ ďĞ
during a chemical reaction (law of conservation of matter). Therefore, ďĂůĂŶĐĞĚ ďĞĐĂƵƐĞ ƚŚĞ ůĂǁ ŽĨ
balancing of a chemical equation is necessary because no matter (hence, ĐŽŶƐĞƌǀĂƟŽŶ ŽĨ ŵĂƩĞƌ ŵƵƐƚ ŚŽůĚ
no atom) is lost or gained during a chemical reaction. ŐŽŽĚ ĚƵƌŝŶŐ Ă ĐŚĞŵŝĐĂů ƌĞĂĐƟŽŶ͘

How are chemical equations balanced
Chemical equations are balanced by ad usting the coef cients placed before
the symbols or formulae of the reactants and products. There are two
commonly used methods for the balancing of chemical equations.
ƒ Hit-and-trial method ƒ Partial equation method
However, at this stage only the hit-and-trial method is described.
What is hit-and-trial method

This method is also called trial-and-error method or inspection method. In
this method, coef cients before the formulae or symbols of the reactants and ĂůĂŶĐŝŶŐ ŽĨ ĐŚĞŵŝĐĂů ĞƋƵĂƟŽŶ
ŝƐ ŶĞĐĞƐƐĂƌLJ ďĞĐĂƵƐĞ ĂƚŽŵƐ ĂƌĞ
products are adjusted in such a way that the total number of atoms of each ŶĞŝƚŚĞƌ ĐƌĞĂƚĞĚ ŶŽƌ ĚĞƐƚƌŽLJĞĚ
element on both the sides become equal. This is called material balance or ĚƵƌŝŶŐ Ă ĐŚĞŵŝĐĂů ƌĞĂĐƟŽŶ͘ dŚƵƐ͕
mass balance. ƚŚĞ ďĂůĂŶĐŝŶŐ ŽĨ ĐŚĞŵŝĐĂů ĞƋƵĂƟŽŶƐ
The following order is found helpful in the balancing of chemical ŝƐ ďĂƐĞĚ ŽŶ ƚŚĞ ůĂǁ ŽĨ ĐŽŶƐĞƌǀĂƟŽŶ
equations by hit-and-trial method: ŽĨ ŵĂƩĞƌͬŵĂƐƐ͘
ƒ Start balancing from the element (other than oxygen and hydrogen)
which appears least in the chemical equation.
ƒ Balance oxygen
ƒ Balance hydrogen
ƒ Check to be sure that the chemical equation is balanced.
Balancing of a chemical equation by the hit-and-trial method involves
a number of steps. The steps involved in the reaction involving the burning
of methane gas in the excess of air (or oxygen) to form carbon dioxide gas
and water are illustrated below:
The reaction is,
Methane + Oxygen (from air) o Carbon dioxide + Water

Step 1. The skeleton equation for this reaction in terms of symbols and formulae
is,
CH (I) + O (I) o CO (I) + 2H O(N)
4
2
2
2
Step 2. Write the number of atoms of each element on both the sides of the
arrow (o) in the above equation as follows:
No. of atoms on the
Element
left (reactant side) right (product side)
C 1 1
H 4 2
O 2 3
As the number of atoms of H and O on both the sides are not equal, the
skeleton equation is not a balanced chemical equation.