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Standard Cell Potential from Half-Cells

Ecell∘=Ecathode∘−Eanode∘E^{\circ}_{\text{cell}} = E^{\circ}_{\text{cathode}} - E^{\circ}_{\text{anode}}

Worked example: Daniell cell: +0.34 V cathode, -0.76 V anode → 1.10 V — press Try an example to run it live, then adjust anything.

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See also
Gibbs Free Energy from Cell Potential (ΔG° = −nFE°) — What that voltage is worth in energy per mole, and whether the reaction runs on its own.
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Standard Cell Potential from Half-Cells explained

E°cellE°anodeE°cathode

Every half-cell potential in the standard tables is quoted as a reduction potential against the standard hydrogen electrode, arbitrarily pinned at 0.000 V. To assemble a cell, pick which electrode is reduced (the cathode) and subtract the other's tabulated value: the Daniell cell puts Cu²⁺/Cu at +0.34 V against Zn²⁺/Zn at −0.76 V, giving 0.34 − (−0.76) = 1.10 V. A positive result means the cell runs spontaneously as written; a negative one means you have the electrodes backwards.

Two traps catch almost everyone. First, do not flip the sign of the anode value before subtracting — the minus in the formula already does that, and doing it twice cancels the reaction. Second, never multiply a half-cell potential by its stoichiometric coefficient: potential is energy per coulomb, an intensive property, so balancing 2Ag⁺ + Cu → 2Ag + Cu²⁺ leaves silver's +0.80 V untouched and the cell delivers 0.80 − 0.34 = 0.46 V. It is ΔG = −nFE°, not E° itself, that scales with the amount of reaction.

Standard Cell Potential from Half-Cells formula

Ecell∘=Ecathode∘−Eanode∘E^{\circ}_{\text{cell}} = E^{\circ}_{\text{cathode}} - E^{\circ}_{\text{anode}}
Where
  • Ecell∘E^{\circ}_{\text{cell}}= Standard cell potential (V)
  • Ecathode∘E^{\circ}_{\text{cathode}}= Cathode standard reduction potential (V)
  • Eanode∘E^{\circ}_{\text{anode}}= Anode standard reduction potential (V)

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Part of this formula set

The electrochemistry equations

3 formulasStandard cell potential from half-cells, the Nernst correction for real conditions, and Faraday's law for plating mass.