Predicting Cell Voltage from E° Tables

Lesson notes

Key points

• A standard reduction potential, E°, measures how strongly a half-cell gains electrons relative to the standard hydrogen electrode, set at zero volts.
• The cell potential equals the cathode's E° minus the anode's E°, both written as reductions.
• With copper at +0.34 volts and zinc at −0.76 volts, the Daniell cell gives 1.10 volts.
• A common exam mistake is multiplying E° by stoichiometric coefficients; potentials are intensive, so never scale them.

Definitions

E° (standard reduction potential)

Tendency of a species to be reduced at 1 M, 1 bar, 25 °C, measured against the SHE (0.00 V).

Takeaway: E°cell = E°cathode − E°anode; never scale potentials.

Reduction potentialE°cellWorked exampleIntensive property