Standard Redox Potential (E°cell) Calculator

Standard Redox Potential (E°cell) Calculator

Volts
Volts

Enter the standard reduction potentials for both half-reactions.

What is Standard Cell Potential?

The Standard Cell Potential (E°cell) is the potential difference (voltage) between the two half-cells of an electrochemical cell operating under standard conditions (25°C, 1 M concentrations, 1 atm pressures). It represents the driving force for electrons to flow in a redox (reduction-oxidation) reaction.

It is calculated using the standard reduction potentials (E°) of the two half-reactions involved:

E°cell = E°cathode - E°anode

Where E°cathode is the standard reduction potential of the species being reduced (at the cathode) and E°anode is the standard reduction potential of the species being oxidized (at the anode). Note that we always subtract the anode's reduction potential.

The sign of E°cell indicates the spontaneity of the reaction under standard conditions:
• E°cell > 0 (Positive): The reaction is spontaneous as written (Galvanic/Voltaic cell).
• E°cell < 0 (Negative): The reaction is non-spontaneous as written; energy must be supplied (Electrolytic cell). The reverse reaction is spontaneous.
• E°cell = 0: The reaction is at equilibrium under standard conditions.

Frequently Asked Questions

What's the difference between a cathode and an anode?

In electrochemistry:
• The Cathode is the electrode where reduction occurs (gain of electrons).
• The Anode is the electrode where oxidation occurs (loss of electrons).
A simple mnemonic is "Red Cat" (Reduction at Cathode) and "An Ox" (Anode Oxidation). In a spontaneous (galvanic) cell, the cathode is the positive terminal and the anode is the negative terminal. In a non-spontaneous (electrolytic) cell, this is reversed.

What is the Standard Hydrogen Electrode (SHE)?

Individual half-cell potentials cannot be measured directly. Therefore, a reference electrode is needed. The Standard Hydrogen Electrode (SHE) is the universally accepted reference, defined as having a standard reduction potential of exactly 0.00 Volts at standard conditions (25°C, 1 atm H₂(g), 1 M H⁺(aq)). All other standard reduction potentials are measured relative to the SHE.

Where do I find standard reduction potentials?

Standard reduction potentials (E°) are experimentally determined values that must be looked up in reference tables, typically found in chemistry textbooks or online databases. They are usually listed for reduction half-reactions. The species with the more positive E° value is more easily reduced and will typically act as the cathode in a spontaneous cell.