Cell Potential
Definition and meaning of Cell Potential in chemistry.
Cell potential is the difference in electric potential between the cathode and anode of an electrochemical cell, which provides the driving force for electrons to flow through the external circuit during a redox reaction.
In more detail
Measured in volts, cell potential (E_cell) reflects the maximum electrical work the cell can perform per unit charge. Under standard conditions (1 M solute concentrations, 1 atm gas pressures, 25 °C), it is called the standard cell potential, E°cell, and is calculated as E°cathode − E°anode using tabulated standard reduction potentials. A positive E°cell signals a spontaneous (galvanic) reaction, while a negative value means the reverse process is favored, requiring an external power source to drive it (electrolysis). At non-standard concentrations, the Nernst equation adjusts E_cell accordingly.
Key facts
| Symbol | E_cell (E°cell for standard conditions) |
|---|---|
| Unit | volt (V) |
| Key formula | E°cell = E°cathode − E°anode |
| Field | Physical Chemistry |
For the Zn/Cu galvanic cell, E°cell = E°(Cu²⁺/Cu) − E°(Zn²⁺/Zn) = 0.34 V − (−0.76 V) = 1.10 V, matching the well-known voltage of this classic reaction.
Frequently asked questions
How is cell potential related to Gibbs free energy?
ΔG° = −nFE°cell, where n is the moles of electrons transferred and F is Faraday's constant (96,485 C/mol). A positive E°cell gives a negative ΔG°, confirming the reaction is thermodynamically spontaneous.
Is cell potential the same as electromotive force (EMF)?
They are used interchangeably in practice; EMF technically denotes the cell potential measured under zero-current, open-circuit conditions, avoiding voltage loss from internal resistance.