Library / Foundations: Chemistry / FCH-26
Foundations: Chemistry
Electrochemical cell potential
Voltage of a cell from the standard electrode potentials of its two half-cells.
- Ref
- FCH-26
- Rev
- v1
- Field
- Foundations: Chemistry
- Result
- Ecell [V]
Use standard electrode potentials E° in volts from a data table. The more positive half-cell is the positive electrode (reduction) and the other the negative (oxidation), so E°cell is the larger minus the smaller. A positive value means the reaction is feasible.
The cell voltage is the difference between its two half-cell potentials.
Calculator
- Voltage of 3 cells in series3.3 V
- Free energy per mole for n = 2−212.3 kJ/mol
What drives the result
Each variable is moved across its typical range while the others stay at the values above. The longest bar is the key driver.
- A positive E°cell means the reaction can run spontaneously, so Zn displaces Cu²⁺.
- The cell voltage and ΔG are linked by ΔG = −nFE.
Chart data as tables
Ranked variables
| Variable | Typical range | Lowest result | Highest result | Swing (V) | Local step | Change in result |
|---|---|---|---|---|---|---|
| Epos Positive electrode | −3.1 to 3 V | −2.34 | 3.76 | 6.1 | +10% | +3.09 % |
| Eneg Negative electrode | −3.1 to 3 V | −2.66 | 3.44 | 6.1 | +10% | +6.91 % |
Sweep of Positive electrode
| Positive electrode (V) | Cell potential (V) |
|---|---|
| −3.1 | −2.34 |
| −2.338 | −1.578 |
| −1.575 | −0.815 |
| −0.8125 | −0.0525 |
| −0.05 | 0.71 |
| 0.7125 | 1.472 |
| 1.475 | 2.235 |
| 2.237 | 2.997 |
| 3 | 3.76 |
Sweep one variable
Variables and how each one contributes
Cell potential
What the equation gives you. Everything else feeds it.
Positive electrode
Standard potential of the half-cell that is reduced (Cu²⁺/Cu = +0.34). Raises the cell voltage one-for-one.
Negative electrode
Standard potential of the half-cell that is oxidised (Zn²⁺/Zn = −0.76). Lowers the cell voltage one-for-one.
Worked example with the values above
- Epos = 0.34 V; Eneg = −0.76 V.
- Subtract: 0.34 − (−0.76).
- Ecell = 1.1 V (the Daniell cell, Zn–Cu).
Assumptions and limits
- Standard conditions (1 mol/dm³, 298 K).
- No current drawn.
Common mistakes
- Subtracting the wrong way round.
- Multiplying E° by the coefficients (it is not scaled).
Statistics and uncertainty
Real cell voltages differ from standard values with concentration and temperature (Nernst equation), often by tens of millivolts.
Where it is used
- Battery and fuel-cell design.
- Predicting corrosion and displacement reactions.
Maths you need
- Redox: oxidation and reduction
- Standard electrode potentials: data table