Chemistry : Balancing Chemical Equations

How to Balance a Chemical Equation?

A chemical equation must be balanced in accordance with the Law of Conservation of Matter. The Law states that matter is neither created nor destroyed during the chemical change that occurs in a chemical reaction. So, the total mass of reactants must equal the total mass of products in a balanced chemical equation.

In a balanced chemical equation, the number of atoms of each element in the reactants equals the number of atoms of each element in the products, since atoms are neither created nor destroyed.

Example:

Word Equation :
Ferric sulfate + Water + Sulfur dioxide → Ferrous sulfate + Sulfuric acid
Molecular Equation :
___ Fe₂(SO₄)₃ + ___ H₂O + ___ SO₂ → ___ FeSO₄ + ___ H₂SO₄
No of atoms : 2 Fe , 4 S , 2 H, 15 O → 1 Fe , 2 S, 2 H, 8 O

Balance Fe atoms : ___ Fe₂(SO₄)₃ + ___ H₂O + ___ SO₂ → 2 FeSO₄ + ___ H₂SO₄
No of atoms : 2 Fe , 4 S , 2 H, 15 O → 2 Fe , 3 S, 2 H, 12 O

Balance S atoms : ___ Fe₂(SO₄)₃ + ___ H₂O + ___ SO₂ → 2 FeSO₄ + 2 H₂SO₄
No of atoms : 2 Fe , 4 S , 2 H, 15 O → 2 Fe , 4 S, 4 H, 16 O

Balance H atoms : ___ Fe₂(SO₄)₃ + 2 H₂O + ___ SO₂ → 2 FeSO₄ + 2 H₂SO₄
No of atoms : 2 Fe , 4 S , 4 H, 16 O → 2 Fe , 4 S, 4 H, 16 O

Balanced Equation : Fe₂(SO₄)₃ + 2 H₂O + SO₂ → 2 FeSO₄ + 2 H₂SO₄
Thus, the stoichiometric coefficients in the balanced equation are
1 [for Fe₂(SO₄)₃], 2 [for H₂O], 1 [for SO₂], 2 [for FeSO₄] and 2 [for H₂SO₄].

Question : What numbers (stoichiometric coefficients) fill the blanks in the balanced molecular equation?
Answer : 1,2,1,2,2.