In a galvanic cell consisting of Cu2+/Cu and Zn2+/Zn, what is the overall reaction and is E°cell positive or negative?

• A. Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s); E°cell > 0
• B. Cu(s) + Zn2+(aq) → Cu2+(aq) + Zn(s); E°cell > 0
• C. Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s); E°cell < 0
• D. Cu(s) + Zn2+(aq) → Cu2+(aq) + Zn(s); E°cell < 0

Answer: (A)

Spontaneous redox in a galvanic cell is driven by the comparison of standard reduction potentials: the species with the higher reduction potential is reduced at the cathode, while the other is oxidized at the anode. For copper and zinc, Cu2+/Cu has a reduction potential of +0.34 V, while Zn2+/Zn is -0.76 V. Therefore copper ions are reduced and zinc metal is oxidized. The overall reaction is Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s). The standard cell potential is E°cell = E°cathode - E°anode = 0.34 - (-0.76) = +1.10 V, which is positive, indicating a spontaneous galvanic cell reaction. Any alternative arrangement that would require copper metal to be oxidized or would reverse the electron flow would yield a negative E°cell and would not occur spontaneously under standard conditions.