How this calculator works
This form describes Ox + n electrons in equilibrium with Red, with unit coefficients for the oxidized and reduced species. Enter dimensionless activities, using one for a pure solid or liquid. For a more complicated half-reaction, include all activity powers in the reduced and oxidized activity products. Standard potential must use the same temperature and reference electrode as the desired potential. Ideal dilute concentrations can approximate activities after division by the standard concentration.
Formula
E = Estandard - (RT/nF) ln(areduced/aoxidized). At 298.15 K, RT ln(10)/F is about 0.05915935 V.
Worked example
At equal reduced and oxidized activities, E = Estandard. At 298.15 K, one electron and activity quotient 10, a standard potential of 0.5 V becomes about 0.440841 V.
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Frequently asked questions
Which logarithm is used?
The calculation uses natural logarithms with RT/nF. A base-10 version needs an extra ln(10) factor.
What activity should I use for a pure metal?
Use one when the pure solid is in its reference state.
Can I enter concentrations directly?
Only as an ideal approximation after normalizing to the appropriate standard concentration.