Nernst Equation Calculator

The Nernst equation adjusts cell potential for non-standard concentrations: E = E_standard - (R*T/(n*F)) * ln(Q). At 25 degC this simplifies to: E = E_standard - (0.05916/n) * log10(Q), where Q is the reaction quotient (concentrations of products over reactants, each raised to stoichiometric powers). At equilibrium, E = 0 and Q = K.

Q = [products]^stoich / [reactants]^stoich, using current concentrations (not equilibrium). For Zn + Cu2+ to Zn2+ + Cu: Q = [Zn2+]/[Cu2+]. Pure solids and liquids are excluded (activity = 1). Increasing [Cu2+] decreases Q, which increases E (more favorable). Increasing [Zn2+] increases Q, which decreases E.

From the Nernst equation: increasing product concentration (numerator of Q) decreases E. Increasing reactant concentration (denominator of Q) increases E. This is consistent with Le Chatelier's principle: increasing products shifts equilibrium backward, reducing the driving force. Concentration cells exploit this: identical electrodes in different concentrations generate a non-zero potential.

A concentration cell has the same electrode material in both half-cells but at different ion concentrations. E_standard = 0 (since both half-reactions are identical). The Nernst equation gives: E = (0.05916/n) * log10([high]/[low]) at 25 degC. The cell delivers energy as the concentrations equalize toward equilibrium. Used in analytical chemistry and as a model for biological membrane potentials.

The temperature term (R*T/(n*F)) appears explicitly. At 25 degC (298.15 K): RT/F = 0.02569 V. At higher temperatures, the correction term (RT/nF * lnQ) is larger, making concentration effects more significant. At lower temperatures, the correction is smaller. For every 10 degC increase, RT/F increases by about 3.4% (0.000862 V/degC).