Standard electrochemical cell potential
Standard cell potential is the potential difference between cathode and anode half-cells under specified standard conditions. Tables normally list both half-reactions as reduction potentials.
The calculator subtracts the anode reduction potential from the cathode reduction potential. It does not multiply potential by stoichiometric coefficients because electrode potential is an intensive property.
How to use the cell potential calculator
- Select the unknown: Choose cell, cathode, or anode standard potential.
- Enter reduction potentials: Use values from the same reference scale and preserve negative signs.
- Calculate: Generate the missing voltage using E°cell = E°cathode − E°anode.
- Interpret conditions: Use the Nernst equation when concentrations, activities, gas pressures, or temperature differ from standard conditions.
Formula and variables
Use tabulated reduction potentials for both electrodes, then subtract the anode value from the cathode value.
E°cell = E°cathode − E°anode- E°cell — Standard cell potential
- Potential difference of the complete cell (V)
- E°cathode — Cathode reduction potential
- Standard reduction potential where reduction occurs (V)
- E°anode — Anode reduction potential
- Tabulated reduction potential for the half-cell that operates in reverse (V)
Zinc–copper galvanic cell
Copper has E°red = +0.34 V and zinc has E°red = −0.76 V.
- Cathode
- Cu²⁺/Cu: +0.34 V
- Anode
- Zn²⁺/Zn: −0.76 V
- E°cell = 0.34 − (−0.76)
- E°cell = 1.10 V
Result: The standard cell potential is 1.10 V.
A positive standard potential is consistent with the written galvanic-cell reaction being thermodynamically favorable under standard conditions.
Understanding your results
Sign and spontaneity
For the reaction as written, positive E°cell corresponds to negative standard Gibbs energy through ΔG° = −nFE°cell.
- Do not multiply E° by balanced-reaction coefficients.
- Reversing the overall reaction changes the sign of E°cell.
- Actual terminal voltage also includes nonstandard conditions, kinetics, and internal losses.
Assumptions
- Both electrode values are standard reduction potentials on the same reference scale.
- The cathode and anode roles match the reaction direction being evaluated.
- Standard-state interpretation is intended.
Limitations
- Does not calculate nonstandard potential, equilibrium constant, Gibbs energy, overpotential, or loaded battery voltage.
- Tabulated values can vary with temperature and chemical form.
Common mistakes
- Adding two reduction potentials without reversing the anode sign convention.
- Multiplying potential by stoichiometric coefficients.
- Dropping a negative sign from a tabulated value.
- Using standard potential to predict actual voltage under load.
Practical use cases
Electrochemistry problems
Check galvanic-cell direction and standard voltage from half-cell tables.
Half-cell comparison
Solve for a missing reduction potential when the other half-cell and total voltage are known.
Frequently asked questions
Why is the anode potential subtracted?
Tables list reduction potentials, but oxidation occurs at the anode; subtracting its reduction potential is equivalent to adding its oxidation potential.
Should electrode potentials be multiplied when balancing electrons?
No. Potential is intensive; use stoichiometric coefficients only when calculating extensive quantities such as Gibbs energy.
What if conditions are not standard?
Use activities or appropriate approximations in the Nernst equation at the relevant temperature.
Sources and review
- Chemistry 2e: Standard Reduction Potentials — OpenStax. Accessed 2026-07-13.
- Electrode potential — IUPAC Compendium of Chemical Terminology. Accessed 2026-07-13.
Reviewed 2026-07-13.