Nernst Equation Calculator
The cell potential away from standard conditions — the Nernst equation, for electrochemistry, pH electrodes and membrane potentials.
E = E° − (RT/nF) ln Q.
How the nernst equation calculator works
E = E° − (RT/nF) ln Q. Concentration shifts the potential logarithmically, so a tenfold change moves it by 59.16/n millivolts at 25 °C.
That 59 mV per decade is why a pH electrode works: each pH unit is a tenfold change in hydrogen ion concentration, and the electrode reports it as 59 millivolts.
Formula: E = E° − (RT/nF) ln Q
Worked examples
| Inputs | Cell potential | Note |
|---|---|---|
| A Daniell cell with Q = 0.1 | 1.12958 V | 1.130 V — 30 mV above standard |
| At standard conditions | 1.1 V | exactly E° |
| A one-electron cell | 0.859159 V | 59 mV per decade |
FAQFrequently asked questions
What is the Nernst equation?
It gives the cell potential away from standard conditions: E = E° − (RT/nF) ln Q.
What is the 59 mV rule?
At 25 °C the potential shifts 59.16/n millivolts for every tenfold change in Q. For a one-electron process that is 59 mV per decade.
How does a pH electrode use it?
Each pH unit is a tenfold change in hydrogen ion activity, which the electrode converts to about 59 mV. The meter is really a very precize voltmeter.
Does temperature matter?
Yes — the slope is proportional to absolute temperature. That is why pH meters have temperature compensation.
Why does a battery go flat?
As it discharges, Q rises toward K and the potential falls. At equilibrium Q = K, E = 0 and no more work can be extracted.
Where these figures come from
- IUPAC — Standard atomic weights (2021 conventional values) — the molar-mass table
- NIST — CODATA 2018 fundamental physical constants — Avogadro constant, gas constant, speed of light
- NIST Chemistry WebBook — thermochemical data
- National Institute of Standards and Technology — the US measurement and reference-data authority
Last checked: September 2026. Atomic masses are the IUPAC conventional values; constants are CODATA 2018; equations are the standard textbook forms.