Standard Electrode Potential (E°)

Standard Electrode Potential (E°) measures the potential of a reversible electrode under standard conditions:

• 1 M concentration of all aqueous species
• 1 atm pressure for gases
• Temperature of 25 °C (298 K)

Definition

The Standard Electrode Potential is the potential of a half-cell measured against the Standard Hydrogen Electrode (SHE), which has a defined potential of 0 V. It shows the tendency of a species to gain electrons (reduction) or lose electrons (oxidation) under standard conditions.

Measurement

To measure standard electrode potential, connect the half-cell of interest to the SHE and record the cell voltage. This measured value represents the electrode potential of the half-cell relative to SHE.

Significance of Standard Electrode Potential

• Predicts the direction of electron flow in electrochemical cells
• A positive E° means strong reduction tendency; a negative E° indicates oxidation tendency
• Helps calculate the electromotive force (EMF) of galvanic cells
• Determines the feasibility and spontaneity of redox reactions

Standard Electrode Potential Table

Scientists tabulate standard electrode potentials with respect to SHE. For example, fluorine has a very positive potential (+2.87 V), showing strong oxidizing power, while alkali metals have highly negative potentials, showing strong reducing ability.

Example

For the half-cell reaction: Cu²⁺ + 2e^– → Cu(s), the standard electrode potential equals +0.34 V. This value shows that copper ions readily gain electrons and get reduced under standard conditions.

Quiz: Standard Electrode Potential

1. What are the standard conditions for measuring standard electrode potential?
2. What is the reference electrode used in measuring standard electrode potentials?
3. What does a positive standard electrode potential signify?
4. Why is the standard electrode potential important in electrochemistry?
5. What is the standard electrode potential of the Standard Hydrogen Electrode (SHE)?

Answers and Explanation

1. 1 M concentration, 1 atm pressure, and 25 °C (298 K)
2. The Standard Hydrogen Electrode (SHE), assigned potential 0 V
3. A strong tendency of the species to undergo reduction (gain electrons)
4. It predicts reaction spontaneity and helps calculate cell voltages
5. By definition, 0 V

To measure E°, you pair the half-cell of interest with the SHE and record the cell voltage. That voltage becomes the standard potential of your half-cell relative to SHE (0 V reference). You can also use alternative reference electrodes (e.g. SCE, Ag/AgCl) after converting to SHE scale. (Reference Electrode — Wikipedia)