How is E°cell computed from a standard reduction potential table?

• A. The table lists oxidation potentials; E°cell = E°anode − E°cathode
• B. The table lists equilibrium constants; E°cell is the average of potentials
• C. The table lists reduction potentials for each couple; E°cell = E°cathode − E°anode
• D. The table lists reaction enthalpies; E°cell is their sum

Answer: (A)

Standard tables list reduction potentials for each redox couple. In a galvanic cell, the cathode is where reduction occurs and the anode is where oxidation occurs. The standard cell potential is found by taking the difference between the cathode’s and the anode’s reduction potentials: E°cell = E°red(cathode) − E°red(anode). This sign convention makes E°cell positive for spontaneous cells. If you tried to use oxidation potentials or mix in enthalpies or equilibrium constants, you’d lose the correct relationship because the tabulated values and the resulting formula rely on reduction potentials. So the correct approach is subtracting the anode’s reduction potential from the cathode’s reduction potential; the other ideas (averaging, summing enthalpies, or using oxidation potentials) do not describe how E°cell is determined from standard potential tables.