Question

In a balanced chemical reaction, equal number of atoms are present on both sides of reaction. A balanced chemical reaction is based on law of conservation of mass which means that total mass of reactants and products participating in a reason must be equal.

(a) Translate the following statement into chemical equation.

• Hydrogen sulphide gas burns in air to give water and sulphur dioxide.

(b) balance the chemical reaction.

Answer 1

(a) The chemical equation for the given chemical reaction is:
${\text{H}}_2\text{S(g)}+{\text{O}}_2\text{(g)}\to {\text{H}}_2\text{O(l)}+{\text{SO}}_2\text{(g)}$

(b) steps to balance a chemical equation
Step-1: write down the unbalanced chemical equation.
${\text{H}}_2\text{S(g)}+3{\text{O}}_2\text{(g)}\to 2{\text{H}}_2\text{O(l)}+2{\text{SO}}_2\text{(g)}$

Step-2: write down the number of atoms of each element present on both reactant and product side in tabular form.
Element reactant side product side

H	1	2
S	1	1
O	2	3

Step-3: add coefficients to balance the atoms present in that one particular molecule in a chemical equation.

• Go by trial and error method. Adding 2 Hydrogen on both sides then it will be 4 on reactants side and on product side 4.
• So 2 H works, 2 hydrogen sulphide, making it 2H₂O
• 3 O₂ then we have 6 oxygen atoms on the reactant side and also 6 oxygen atoms on the product side.

Element reactant side product side

H	4	4
S	2	2
O	6	6

Step-4: write down the balanced chemical equation:
$2{\text{H}}_2\text{S(g)}+3{\text{O}}_2\text{(g)}\to 2{\text{H}}_2\text{O(l)}+2{\text{SO}}_2\text{(g)}$