If Cu2+/Cu (E°red = +0.34 V) and Fe2+/Fe (E°red = -0.44 V) are connected as a galvanic cell, which arrangement yields a positive E°cell?

• A. Fe as cathode and Cu as anode
• B. Cu as cathode and Fe as anode
• C. Fe as both electrodes
• D. Cu as both electrodes

Answer: (B)

The main idea is that a galvanic cell is spontaneous when the electrode with the more positive reduction potential is the cathode (it gets reduced), while the other electrode is oxidized. Copper's Cu2+/Cu couple has E°red = +0.34 V, which is higher than iron's Fe2+/Fe at -0.44 V. So copper should be the cathode and iron the anode. The standard cell potential is E°cell = E°red(cathode) - E°red(anode) = +0.34 - (-0.44) = +0.78 V, a positive value, indicating a spontaneous cell with electron flow from iron to copper. If you reversed them, E°cell would be negative, not spontaneous. If both electrodes were the same metal/redox couple, there would be essentially no driving force (E°cell ≈ 0).