Why is the reaction SO2 + H2O → H2SO2 not balanced?
The Correct Answer and Explanation is:
The reaction SO₂ + H₂O → H₂SO₂ is not balanced because H₂SO₂ is not the correct product of the reaction between sulfur dioxide (SO₂) and water (H₂O). The correct product is sulfurous acid (H₂SO₃), not H₂SO₂. Therefore, the equation is chemically incorrect, not just unbalanced.
✅ Correct Reaction:
SO2+H2O→H2SO3\text{SO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_3
❌ Why SO₂ + H₂O → H₂SO₂ is incorrect:
- Incorrect formula of the product:
- H₂SO₂ suggests a sulfurous compound with an oxidation state of +2 for sulfur, which is uncommon and unstable under normal conditions.
- The known and stable oxoacid formed when sulfur dioxide dissolves in water is sulfurous acid (H₂SO₃), in which sulfur has a +4 oxidation state.
- Redox inconsistency:
- SO₂ is already in the +4 oxidation state. Forming H₂SO₂ implies an oxidation state of +2 for sulfur, which would require a reduction, but water alone cannot act as a reducing agent in this reaction.
- Molecular structure mismatch:
- H₂SO₃ has a known molecular structure consistent with oxoacids (two OH groups and one =O double bond to sulfur). H₂SO₂ lacks such a recognized stable structure.
✅ Balanced and Correct Reaction:
SO2+H2O→H2SO3\text{SO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_3
This reaction is already balanced in terms of atoms (S:1, O:3, H:2) and charge (all species are neutral).
Summary:
The reaction SO₂ + H₂O → H₂SO₂ is not balanced because H₂SO₂ is not the correct chemical product. The actual reaction produces H₂SO₃ (sulfurous acid), which is both chemically valid and properly balanced.
