Question

How to balance that equation

Answer 1

The balanced equation is

Cl₂ + SO₂ +2H₂O ⟶ 2Cl⁻ +SO₄²⁻ + 4H⁺

This is a redox reaction, so I will balance it using the ion-electron method.

Step 1. Write the skeleton equation.

Strip the equation of H⁺ and H₂O (these come back in during the balancing procedure). We get

Cl₂ + SO₂ ⟶ Cl⁻ +SO₄²⁻

Step 2: Separate the skeleton equation into two half-reactions.

Cl₂ ⟶ Cl⁻

SO₂ ⟶ SO₄²⁻

Step 3: Balance all atoms other than H and O.

Cl₂ ⟶ 2Cl⁻

SO₂ ⟶ SO₄²⁻

Step 4: Balance O.

Add enough H₂O molecules to balance O,

Cl₂ ⟶ 2Cl⁻

SO₂ + 2H₂O ⟶ SO₄²⁻

Step 5: Balance H.

Add enough H⁺ ions to balance H.

Cl₂ ⟶ 2Cl⁻

SO₂ + 2H₂O ⟶ SO₄²⁻ + 4H⁺

Step 6: Balance charge.

Add electrons to the side that needs more negative charge.

Cl₂ + 2e⁻ ⟶ 2Cl⁻

SO₂ + 2H₂O ⟶ SO₄²⁻ + 4H⁺ + 2e⁻

Step 7: Add the two half-reactions.

The balanced equation is

Cl₂ + SO₂ + 2H₂O ⟶ 2Cl⁻ + SO₄²⁻ + 4H⁺