Standard Electrode Potential
Definition and meaning of Standard Electrode Potential in chemistry.
Standard electrode potential is the measured voltage of a half-reaction under standard conditions (25 degrees Celsius, 1 molar concentration, 1 atmosphere pressure) relative to the standard hydrogen electrode, which is defined as 0.00 V.
In more detail
Standard electrode potentials quantify the tendency of a chemical species to accept electrons (undergo reduction). The more positive the potential, the greater the tendency to be reduced and act as an oxidizing agent; the more negative, the greater the tendency to lose electrons and act as a reducing agent. These tabulated values are used to predict spontaneity and feasibility of redox reactions. When two half-reactions are combined, the overall cell potential (E°cell) is calculated by subtracting the reduction potential of the oxidation half-reaction from the reduction potential of the reduction half-reaction. A positive E°cell indicates a spontaneous reaction.
Key facts
| Symbol | E° (E naught) |
|---|---|
| Units | Volts (V) |
| Reference electrode | Standard hydrogen electrode (SHE), assigned 0.00 V |
| Field | Physical Chemistry |
Copper(II) ions are readily reduced with E° = +0.34 V for the half-reaction Cu2+ + 2e− → Cu, while zinc ions are less readily reduced with E° = -0.76 V for Zn2+ + 2e− → Zn. This difference means Cu2+ is a better oxidizing agent than Zn2+.
Frequently asked questions
How do you determine if a redox reaction is spontaneous?
Calculate the overall cell potential (E°cell) by subtracting the reduction potential of the oxidation half-reaction from the reduction potential of the reduction half-reaction. If E°cell is positive, the reaction is thermodynamically spontaneous.
What are the standard conditions for electrode potential measurements?
Standard conditions are 25 degrees Celsius (298 K), 1 molar concentration for all dissolved species, and 1 atmosphere partial pressure for any gases involved.