General Chemistry • Electrochemistry
Select a standard reduction half-reaction, then enter the temperature, ion concentrations and any relevant gas pressures. The calculator builds the reaction quotient \(Q\) for that electrode and applies the Nernst equation \(E = E^{\circ} - \dfrac{RT}{zF}\ln Q\) to find the electrode potential at the specified conditions.
It is the half-cell potential E when concentrations (activities), gas pressures, or temperature differ from standard conditions. The value is obtained by adjusting the standard reduction potential E° using the reaction quotient Q.
The calculator applies E = E° - (R*T/(z*F)) ln(Q), where z is the number of electrons in the selected balanced half-reaction and Q is built from the entered activities. Changing Q changes the correction term and shifts E relative to E°.
Q is the product of activities of products raised to their stoichiometric powers divided by the same for reactants, using only species with variable activity. Pure solids and liquids are not included because their activity is taken as 1.
No, this page computes a single electrode (half-cell) potential. A full cell potential requires combining a cathode and an anode half-reaction and using Ecell = Ecathode - Eanode.
Concentration (activity) changes Q, and ln(Q) appears in the Nernst correction term. Depending on the half-reaction and whether Q increases or decreases, E can become more positive or more negative relative to E°.