Nernst Equation Calculator

The Nernst equation, E = E° − (RT/nF)·ln(Q), adjusts a half-reaction's standard electrode potential E° (measured at 1 M/1 atm 'standard' conditions) for whatever concentrations or pressures are actually present, summarized by the reaction quotient Q — the same products-over-reactants ratio used in equilibrium calculations, just evaluated before the reaction necessarily reaches equilibrium. R is the molar gas constant, T the absolute temperature, n the moles of electrons transferred per the half-reaction as written, and F the Faraday constant (the charge of one mole of electrons).

This calculator also reports the 'Nernst slope' — RT·ln(10)/(nF), converted to millivolts — which is how much the potential shifts for every tenfold change in Q. For a one-electron transfer at 25°C this works out to the widely-quoted ≈59.2 mV per decade; doubling n (as in this calculator's default, a two-electron transfer) halves that shift, since the same charge now has to move twice the electrons.

Setting Q = 1 (products and reactants at standard conditions) makes ln(Q) = 0, so the equation correctly reduces to E = E° — useful as a sanity check before changing Q to see how far off standard conditions actually shift the potential.