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 upper B r superscript minus right arrow upper B r subscript 2 plus 2 e superscript minus. Second line: upper C l subscript 2 plus 2 e superscript minus right arrow 2 upper C l superscript minus.

What should he write as the final, balanced equation?
Upper C l subscript 2 plus 2 upper B r superscript minus right arrow upper B r subscript 2 plus 2 upper C l superscript minus.
Upper C l subscript 2 plus 2 upper B r superscript minus, plus 2 e superscript minus right arrow upper B r subscript 2 plus 2 upper C l superscript minus.
Upper C l subscript 2 plus 2 upper B r superscript minus right arrow upper B r subscript 2 plus 2 upper C l superscript minus, plus 2 e superscript minus.
Upper C l subscript 2 plus upper B r superscript minus plus 2 e superscript minus right arrow upper B r subscript 2 plus upper C l superscript minus, plus 2 e superscript minus.

Answer 1

The correct final, balanced equation is:

Cl2 + 2 Br− → Br2 + 2 Cl−

Explanation: add the two half-reactions so the 2 e− cancel; electrons do not appear in the net equation.