Electrochemical Cell Potential Calculator

Calculate the standard cell potential E°cell from the reduction potentials of the cathode and anode half-reactions.

Thermodynamics

Entrée

Common half-cells

Résultat

How to Use

  1. 1
    Look up standard reduction potentials

    Find the standard reduction potentials (E°red) for both half-reactions in your electrochemical cell from a standard reference table.

  2. 2
    Enter both half-cell potentials

    Input E°red for the cathode (reduction half-reaction) and the anode (oxidation half-reaction). The tool automatically handles the sign reversal for the oxidation half.

  3. 3
    Read cell potential and spontaneity

    The result displays E°cell = E°cathode - E°anode, the standard free energy change ΔG° = -nF×E°, and whether the cell reaction is spontaneous.

About

Electrochemical cell potential quantifies the thermodynamic driving force for an oxidation-reduction reaction occurring in an electrochemical cell. It is rooted in the tendency of different elements and compounds to accept or donate electrons — quantified as standard reduction potentials on the electrochemical series anchored to the standard hydrogen electrode.

The half-reaction framework allows any overall redox reaction to be decomposed into two electrode processes: reduction at the cathode (electrons consumed) and oxidation at the anode (electrons released). The standard cell potential E°cell = E°cathode - E°anode immediately reveals whether a proposed reaction is thermodynamically spontaneous (E°cell > 0) or requires electrical energy input (E°cell < 0, as in electrolysis).

Electrochemical principles underlie a vast range of technologies: galvanic cells (primary batteries from alkaline AA cells to lithium-ion), secondary cells (rechargeable batteries, fuel cells), corrosion science (predicting which metals corrode preferentially in galvanic couples), and electroanalytical chemistry (potentiometry, cyclic voltammetry, electrochemical impedance spectroscopy). This calculator also computes ΔG° and the equilibrium constant K, connecting a simple voltage measurement to the deepest thermodynamic descriptions of chemical equilibria.

FAQ

How is standard cell potential calculated?
Standard cell potential is E°cell = E°cathode - E°anode, where both values are standard reduction potentials (measured versus the standard hydrogen electrode, SHE, which is assigned E° = 0.000 V by convention). A positive E°cell indicates a spontaneous reaction under standard conditions (1 mol/L concentrations, 25°C, 1 atm). For example, the Zn-Cu Daniell cell gives E°cell = 0.337 V - (-0.762 V) = 1.099 V.
What is the standard hydrogen electrode?
The standard hydrogen electrode (SHE) is the universal reference against which all standard reduction potentials are measured. It consists of a platinum electrode immersed in 1 mol/L H⁺ solution with H₂ gas at 1 atm bubbling over it, assigned E° = 0.000 V by definition. In practice, the SHE is difficult to use, so secondary reference electrodes like the saturated calomel electrode (SCE, +0.241 V vs SHE) or silver/silver chloride electrode (+0.197 V vs SHE) are used in the laboratory.
How does cell potential relate to Gibbs free energy?
The relationship is ΔG° = -nFE°cell, where n is the number of moles of electrons transferred and F is Faraday's constant (96,485 C/mol). A positive E°cell corresponds to negative ΔG°, indicating spontaneity — consistent with thermodynamic convention. This relationship connects electrochemistry to thermodynamics, allowing cell potential measurements to determine equilibrium constants via ΔG° = -RT ln K.
What is the Nernst equation?
The Nernst equation corrects cell potential for non-standard concentrations: E = E° - (RT/nF) ln Q, where Q is the reaction quotient. At 25°C this simplifies to E = E° - (0.0592/n) log Q. The Nernst equation explains why a battery’s voltage decreases as it discharges (Q increases as reactants are consumed) and is the basis for ion-selective electrodes used in pH meters and medical diagnostics.
What is the difference between EMF and cell potential?
Electromotive force (EMF) and cell potential are effectively synonymous terms for the voltage produced by an electrochemical cell under zero-current (open-circuit) conditions. EMF is the older term, now largely replaced in IUPAC nomenclature by cell potential (E°cell for standard conditions, Ecell for actual conditions). Terminal voltage under load is always lower than EMF due to internal resistance losses according to V = EMF - I×r, where r is the internal resistance of the cell.
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