Nernst Equation Calculator
Cell potential away from standard conditions, the slope per decade, the Gibbs energy and the equilibrium constant.
Results
Cell potential
1.159159
V
Voltage
0.029580
V/decade
Gibbs free energy
-223.6837
kJ/mol
Equilibrium constant
1.54063e+37
What this tool does
Standard potentials assume everything at one molar, which almost nothing ever is. The Nernst equation corrects for the actual concentrations, and it explains why a battery's voltage sags as it discharges: the products build up, the quotient rises, and the potential falls with it.
Formula
E = E° − (RT ÷ nF) × ln Q
Variables
| Symbol | Meaning | Unit |
|---|---|---|
e0 | Standard potential | V |
nz | Electrons exchanged | — |
qq | Reaction quotient | — |
t | Temperature | °C |
E | Cell potential | V |
SL | Voltage | V/decade |
DG | Gibbs free energy | kJ/mol |
KQ | Equilibrium constant | — |
Worked example
- Standard potential1.1 V
- Electrons exchanged2
- Reaction quotient0.01
- Temperature25 °C
- Cell potential1.159159 V
- Voltage0.029580 V/decade
- Gibbs free energy-223.6837 kJ/mol
- Equilibrium constant1.54063e+37
Limitations
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
Frequently asked questions
What is the 59 mV per decade figure?
It is the second result: how much the potential shifts for each tenfold change in the quotient, for a single-electron process at 25 °C. It is why a pH electrode reads about 59 millivolts per pH unit, and why calibrating one at a different temperature matters — the slope changes with absolute temperature.