Applying the Nernst Equation

Applying the Nernst equation means writing the reaction quotient Q from the actual, nonstandard concentrations present, substituting Q, the electron count n, and temperature into Ecell = E°cell − (RT/nF) ln Q, and solving for Ecell.

For a cell with E°cell = −0.146 V, n = 2, and Q = 2.5 × 10³ at 298 K, Ecell = −0.146 − [(8.314)(298)/(2)(96,485)] ln(2.5 × 10³) ≈ −0.146 − 0.101 ≈ −0.247 V, remaining nonspontaneous under these particular nonstandard conditions, and, notably, more negative than E°cell itself rather than less. That direction depends entirely on Q's value relative to 1; a Q below 1 would have shifted Ecell the other way, toward less negative.