Nernst Equation Calculator
Find the actual cell potential under non-standard conditions from the standard potential, electrons transferred, reaction quotient and temperature.
How it works
E = E° − (R·T / n·F)·ln Q · at 298 K ≈ E° − (0.0592 / n)·log₁₀ Q
The Nernst equation corrects a cell’s standard potential for the real concentrations (or pressures) of the species, captured in the reaction quotient Q. As a reaction proceeds and Q rises, the potential falls; at equilibrium Q equals K and the potential reaches zero — the battery is dead. At 25 °C the constants collapse into the handy form E = E° − (0.0592/n)·log₁₀Q.
Worked example
A Daniell cell has E° = 1.10 V with n = 2 electrons. If Q = 1 (all species at unit activity), the log term is zero and E = 1.10 V. Raise Q to 100 and E = 1.10 − (0.0592/2)·log₁₀(100) = 1.10 − 0.059 = 1.041 V.
Sources: Nernst equation — Wikipedia
Frequently asked questions
What is the reaction quotient Q?
Q has the same form as the equilibrium constant K but uses the current concentrations and pressures rather than equilibrium ones. It measures how far, and in which direction, the reaction is from equilibrium.
Why does E fall as the reaction runs?
As products build up, Q increases and the (RT/nF)·ln Q term grows, subtracting more from E°. When Q reaches K the cell potential is zero and no more useful work can be extracted.
When can I use the 0.0592/n shortcut?
Only at 298 K (25 °C). It bundles R, F, the temperature and the conversion from ln to log₁₀ into one number. At other temperatures use the full RT/nF form, as this calculator does.
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This calculator is for educational purposes. Double-check important results before acting on them.