Question

Balance the following equation stepwise.

SO_2(g) + H₂S_(aq) → S_(s) + H₂O_(I)

Answer 1

Step 1:

Rewrite the given equation as it is

SO_2(g) + H₂S_(aq) → S_(s) + H₂O_(I)

Step 2:

Write the number of atoms of each element in the unbalanced equation on both sides of equations.

Element	Number of atoms in reactants (left side)	Number of atoms in products (right side)
S	2	1
O	2	1
H	2	2

The number of hydrogen atoms on both sides of the equation is same, therefore, equalise the number of sulphur atoms and oxygen atoms.

Step 3: To balance the number of sulphur atoms:

To equalise the number of sulphur atoms, we use 2 as the factor in the product, now the equation becomes

SO₂ + H₂S → 2S + H₂O

Step 4:

To equalise the number of oxygen atoms in the unbalanced equation.

Number of atoms of oxygen	In reactants (SO2)	In products H2O
Initially	2	1
To balance	2	1 × 2

To equalise the number of sulphur atoms, we use 2 as the factor in the product i.e. H₂O, now the unbalanced equation becomes

SO₂ + H₂S → 2S + 2H₂O

Step 5:

To equalise the number of hydrogen atoms in unbalanced equation:

Number of atoms of hydrogen	In reactants (H2S)	In products (H2O)
Initially	2	4
To balance	2 × 2	4

To equalise the number of hydrogen atoms we use 2 as the factor in the reactant i.e, H₂S, now the unbalanced equation become

SO₂ + H₂S → 2S + 2H₂O

Now, count the atoms of each element on both sides of the equation, there are less number of sulphur atoms in the product. Now equalise the sulphur atoms, the balanced equation becomes,

SO₂ + H₂S → 2S + 2H₂O

Now indicate the physical states of reactants and products.

SO_2(g) + 2H₂S_(aq) → 3S_(s) + 2H₂O_(I)