Electrode Potential
Definition and meaning of Electrode Potential in chemistry.
Electrode potential is the potential difference that develops at the interface between an electrode and the electrolyte solution surrounding it, arising from the tendency of a redox half-reaction to gain or lose electrons.
In more detail
Because a single electrode's potential cannot be measured in isolation, it is defined relative to the standard hydrogen electrode (SHE), which is arbitrarily assigned 0.00 V. Values measured under standard conditions (298 K, 1 mol/L ion concentration, 1 atm gas pressure) are called standard electrode potentials, E°, and are conventionally tabulated as reduction potentials. Comparing E° values predicts which species will be oxidized or reduced when two half-cells are connected, and the overall cell potential equals E°cathode minus E°anode. Non-standard conditions are handled with the Nernst equation.
Key facts
| Field | Physical Chemistry |
|---|---|
| Reference electrode | Standard hydrogen electrode (SHE), E° = 0.00 V |
| Standard conditions | 298 K, 1 mol/L, 1 atm |
| Symbol | E (electrode potential), E° (standard electrode potential), units: volts (V) |
In the Daniell cell, Zn2+/Zn has E° = -0.76 V and Cu2+/Cu has E° = +0.34 V. Since copper's potential is higher, Cu2+ is reduced (cathode) while zinc is oxidized (anode), giving a cell potential of 0.34 - (-0.76) = 1.10 V.
Frequently asked questions
What does a negative standard electrode potential mean?
It means the half-reaction is less likely to be reduced than H+/H2 and the species is a stronger reducing agent than hydrogen, so it more readily undergoes oxidation.
How do electrode potentials relate to cell EMF?
The overall cell potential is calculated as E°cell = E°cathode - E°anode, using the standard reduction potentials of the two half-cells.