Cell Potential (also known as electromotive force or EMF) is the measure of the potential difference between two half-cells in an electrochemical cell. It represents the 'pull' or 'push' on electrons in a redox reaction.

It is the force that drives the flow of electrons from the anode (oxidation) to the cathode (reduction).

Cell potential is measured in Volts (V). A positive cell potential indicates a spontaneous reaction (a galvanic or voltaic cell), while a negative cell potential indicates a non-spontaneous reaction (an electrolytic cell).

To compare the potentials of different half-reactions, scientists use Standard Electrode Potentials (E°).

These are measured under standard conditions (25°C, 1 M concentration for solutions, 1 atm pressure for gases).

By convention, standard electrode potentials are written as reduction potentials. The reference point is the Standard Hydrogen Electrode (SHE), which is assigned a potential of exactly 0 V.

A more positive E° value means the substance is more likely to be reduced (act as an oxidizing agent). A more negative E° value means it is more likely to be oxidized (act as a reducing agent).

The standard cell potential for a reaction can be calculated by combining the standard reduction potentials of the two half-reactions.

The formula is: E°cell = E°cathode - E°anode

Where:

E°cathode: The standard reduction potential of the substance being reduced (the half-reaction with the higher E° value).

E°anode: The standard reduction potential of the substance being oxidized (the half-reaction with the lower E° value).

Important: Even though the anode is where oxidation occurs, you still use its standard *reduction* potential in this formula.

When conditions are not standard (concentrations are not 1 M), the cell potential changes. The Nernst Equation is used to calculate the cell potential (Ecell) under non-standard conditions.

The equation is: Ecell = E°cell - (RT/nF)lnQ

R: The ideal gas constant (8.314 J/(mol·K)).

T: Temperature in Kelvin.

n: The number of moles of electrons transferred in the balanced redox reaction.

F: Faraday's constant (96,485 C/mol e⁻).

Q: The reaction quotient, which is the ratio of product concentrations to reactant concentrations at that moment.

Cell potential is the principle that makes all batteries work.

Batteries: A battery is a galvanic cell (or a series of them) that uses a spontaneous chemical reaction to produce a positive cell potential, pushing electrons through an external circuit to power a device.

Corrosion: The rusting of iron is an electrochemical process. Small galvanic cells form on the surface of the metal, where iron acts as the anode and is oxidized. Understanding cell potentials helps in developing methods for corrosion prevention, such as cathodic protection.