Electrode Potential
Definition and meaning of Electrode Potential in chemistry.
Electrode potential is a measure of a chemical species' tendency to gain or lose electrons at an electrode, expressed in volts and measured relative to the standard hydrogen electrode (SHE).
In more detail
Each half-reaction has a characteristic potential (measured in volts) that indicates its tendency to occur. Standard electrode potential (E°) is the electrode potential measured under standard conditions: 25°C, with all species at 1 M concentration and gases at 1 atm pressure. Positive potentials indicate a stronger tendency to gain electrons (reduction), making those species better oxidizing agents. Negative potentials indicate a stronger tendency to lose electrons (oxidation), making those species better reducing agents. Electrode potentials allow chemists to predict whether redox reactions occur spontaneously and to calculate the cell voltage in electrochemical cells.
Key facts
| Field | Physical Chemistry |
|---|---|
| Standard reference | Standard hydrogen electrode (SHE): E° = 0 V |
| Unit | Volts (V), millivolts (mV) |
| Sign interpretation | Positive E° favors reduction; negative E° favors oxidation |
The copper half-reaction Cu2+ + 2e- → Cu has a standard electrode potential of +0.34 V, while the zinc half-reaction Zn2+ + 2e- → Zn has a standard electrode potential of -0.76 V. Since copper's potential is higher, Cu2+ ions are more easily reduced than Zn2+ ions, and zinc is a stronger reducing agent.
Frequently asked questions
How is standard electrode potential measured?
Standard electrode potential is determined by comparing a half-reaction to the standard hydrogen electrode at 25°C, with all aqueous species at 1 M concentration and all gases at 1 atm pressure.
Can electrode potential predict if a reaction will happen?
Yes. If the overall cell potential (E°cell) is positive, the reaction will occur spontaneously under standard conditions. A negative E°cell indicates the reverse reaction is favorable.