Complete Question:
A student is asked to balance an equation by using the half-reaction method. He determines the two half reactions as shown below.
2 Br⁻ → Br₂ + 2e⁻
Cl₂ + 2e⁻ → 2Cl⁻
What should he write as the final, balances equation ?
Cl₂ + 2Br⁻ → Br₂ + 2 Cl⁻
Cl₂ + 2 Br⁻ + 2 e- → Br₂ + 2 Cl⁻
Cl₂ + 2 Br⁻ → Br₂ + Cl⁻ + 2 e⁻
Cl₂ + Br⁻ + 2e- → Br₂ + Cl⁻ + 2e⁻
Answer:
Cl₂ + 2Br⁻ → Br₂ + 2 Cl⁻ is the correct answer.
Explanation:
First half equation is as
2 Br⁻ → Br₂ + 2e⁻
This is oxidation reaction in which two bromide ions each containing one extra electron combine to form bromine molecule with the removal of two electrons. This removal of electrons is called as oxidation.
Second half equation is as
Cl₂ + 2e⁻ → 2Cl⁻
This is reduction reaction in which one molecule of chlorine gains two electrons and split apart to form two chloride ions. This gain of electrons is called as reduction.
Hence, in overall reaction the two electrons lost by bromine will be gained by the chlorine molecule forming a bromine molecule and a chloride ions. i.e.
Cl₂ + 2Br⁻ → Br₂ + 2 Cl⁻
