What is the formula for standard cell EMF?

E°cell = E°cathode − E°anode, where both values are standard reduction potentials (in volts) from a reduction potential table. The cathode is where reduction occurs (gains electrons) and the anode is where oxidation occurs (loses electrons).

How do I identify the cathode and anode?

The cathode always has the higher (more positive) standard reduction potential. The anode has the lower reduction potential. Electrons flow from anode to cathode through the external circuit.

What does a positive E°cell mean?

A positive E°cell means the forward reaction is spontaneous under standard conditions (25 °C, 1 M, 1 atm). The cell can do useful electrical work and ΔG° is negative.

What does a negative E°cell mean?

A negative E°cell means the reaction is non-spontaneous in the forward direction under standard conditions. An external voltage must be applied to drive the reaction — this is the principle of electrolysis.

How is Gibbs free energy calculated from EMF?

ΔG° = −nFE°cell, where n is the number of moles of electrons transferred and F is Faraday's constant (96,485 C/mol). A negative ΔG° confirms spontaneity and indicates the maximum useful work the cell can perform.

Are these standard or non-standard conditions?

This calculator uses standard conditions: 25 °C (298.15 K), 1 M for all dissolved species, 1 atm for gases. For non-standard conditions (different temperature, concentrations, or pressures), use the Nernst equation calculator instead.

Where can I find standard reduction potentials?

Standard reduction potential tables are in most general chemistry textbooks. Common examples: Zn²⁺/Zn = −0.76 V, Cu²⁺/Cu = +0.34 V, H⁺/H₂ = 0.00 V (reference), Ag⁺/Ag = +0.80 V, F₂/F⁻ = +2.87 V.

Electrochemical Cell EMF Calculator

Name: Electrochemical Cell EMF Calculator
Availability: InStock
Author: Nham Vu

Enter the standard reduction potentials for the cathode and anode half-cells to instantly calculate the standard EMF of the electrochemical cell.

Cell Inputs

E°_cell = E°_cathode − E°_anode

Cathode Reduction Potential (E°_cathode)

Reduction occurs here — higher reduction potential half-cell.

Anode Reduction Potential (E°_anode)

Oxidation occurs here — enter as standard reduction potential.

Electrons Transferred (n)

mol e⁻

Number of moles of electrons in the balanced overall reaction.

Common Cells (click to fill)

Enter half-cell potentials on the left and click Calculate EMF.

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Summary

Enter the standard reduction potentials for the cathode and anode half-cells to instantly calculate the standard EMF of the electrochemical cell.

How it works

Look up the standard reduction potential (E°) for each half-reaction from a standard electrochemistry table.
Enter the cathode (reduction) half-cell potential — this is the half-cell with the higher reduction potential.
Enter the anode (oxidation) half-cell potential — this is the half-cell where oxidation occurs.
Enter the number of electrons (n) transferred in the balanced overall reaction.
Click Calculate; the tool applies E°cell = E°cathode − E°anode and shows EMF, spontaneity, and ΔG°.
Review the breakdown showing each step, the spontaneity verdict, and the standard Gibbs free energy.

Use cases

Determine the voltage of a standard galvanic cell such as the Daniell cell (Zn/Cu).
Predict whether a redox reaction is spontaneous under standard conditions.
Calculate standard Gibbs free energy change (ΔG°) from cell potential.
Solve electrochemistry homework problems and check hand calculations.
Compare multiple electrode combinations to find the highest-voltage cell design.
Understand which half-cell acts as cathode and which acts as anode.
Prepare for AP Chemistry, university general chemistry, or physical chemistry exams.
Verify textbook answers for standard cell potential problems.

Frequently Asked Questions

Related tools

Nernst Equation Calculator Gibbs Free Energy Calculator Half Cell Potential Calculator

Last updated: 2026-05-28 · Reviewed by Nham Vu