What is the standard cell potential for the cell formed by H+ / H2 (E° = 0.00 V) and O2 / H2O (E° = +1.23 V)?

• A. -1.23
• B. 1.23
• C. -2.46
• D. 0.00

Answer: (B)

The standard cell potential comes from the difference between the reduction potentials of the two half-reactions, with the higher value acting as the cathode (reduction) and the lower as the anode (oxidation). Here, the O2/H2O couple has a reduction potential of +1.23 V, while the H+/H2 couple is 0.00 V. Since +1.23 V is more positive, oxygen is reduced at the cathode and hydrogen is oxidized at the anode.

Therefore, E°cell = E°red(cathode) − E°red(anode) = 1.23 V − 0.00 V = +1.23 V. A positive value means the reaction is spontaneous under standard conditions. The overall reaction is 2H2 + O2 → 2H2O.