Balancing of a chemical equation means making the number of atoms of each element equal on both sides of the equation.
The methods of balancing equation are:
1) Hit and Trial Method:
The simplest method to balance a chemical equation is by hit and trial method.
Step 1 : Write down the correct formula of the reactants and products with plus sign in between with an arrow pointing from reactants to Products. This is called skeletal equation.
Step 2: Select the biggest formula from the Skeleton equation and equalise the number of atoms of each of its constituent elements on both sides of the chemical equation by suitable multiplication .
Step 3: When an elementary gas appear as a reactant or a product ,the equation is balanced more easily by keeping the elementary gas in the atomic state. The balanced atomic equation is then made molecular by multiplying the whole equation by 2.
Question : Magnetic oxide when heated with hydrogen is reduced to iron and water is also produced. Write balanced equation for the reaction?
Answer : Magnetic oxide + Hydrogen ———-> Iron + Water
Fe3O4 + H2 ——–> Fe + H2O
To equalise the number of atoms of Fe on both sides, multiply Fe by 3 , we have
Fe3O4 + H2 ——–> 3Fe + H2O
The above equation has 4 atoms of O on L.H.S. and 1 atoms of O on R.H.S.
To equalise, multiply water by 4.
Fe3O4 + H2 ——–> 3Fe + 4H2O
The above equation has 8 H atoms on R.H.S. and 2 H atoms on L.H.S.
To equalise ,multiply H2 on L.H.S. by 4
Fe3O4 + 4H2 ——–> 3Fe + 4H2O
This a balanced chemical equation
2) Partial Equation method
Step 1 The chemical reaction represented by the equation is supposed to proceed in two or more steps.
Step 2 The Skeleton equation representing each step are written and then balanced by hit and trial method. These equations are known as partial equations.
Step 3 If necessary the partial equation are multiplied by suitable integers so as to cancel those intermediate products which do not occur in the final reaction .
Step 4 The partial equations are added up to get the final balanced equation.
Question : The skeleton equation to represent the action of chlorine on a hot solution of sodium hydroxide is
NaOH + Cl2 ————> NaCl + NaClO3 + H20
Balance this equation by the method of partial equations
Answer : Cl2 + H2O ———-> H2O + HClO
NaOH + HCl ————> NaCl + H2O
NaOH + HClO ———–> NaClO + H2O
3 NaClO ———–> 2 NaCl + NaClO3
3 Cl2 + 6 NaOH ————> 5 NaCl + NaClO3 + 3 H2O