Question

Consider the half reactions below for a chemical reaction.

Upper Z n right arrow upper Z n superscript 2 plus (a q) plus 2 e superscript minus. Second line: upper C u superscript 2 plus (a q)plus 2 e superscript minus right arrow upper C u (s).

What is the overall equation for this chemical reaction?
Upper Z n (s) plus upper C u superscript 2 plus (a q) right arrow upper Z n superscript 2 plus (a q) plus upper C u (s).
Upper Z n (s) plus upper C u superscript 2 plus (a q) right arrow upper C u superscript 2 plus (a q) plus upper Z n (s).
Upper Z n superscript 2 plus (a q) plus upper C u (s) right arrow upper C u superscript 2 plus (a q) plus upper Z n (s).
Upper Z n superscript 2 plus (a q) plus 2 e superscript minus right arrow upper C u superscript 2 plus (a q) plus 2 e superscript plus.

Answer 1

The correct overall equation is:

Zn(s) + Cu^2+(aq) → Zn^2+(aq) + Cu(s)

Reason: Zn is oxidized (Zn → Zn^2+ + 2e−) and Cu^2+ is reduced (Cu^2+ + 2e− → Cu). Adding the half-reactions cancels the 2 e− and gives the net equation above.