Calculator Inputs
Use reduction potentials from a standard electrochemical table. The temperature field affects the equilibrium constant estimate displayed here.
Example Data Table
These sample rows help verify the calculator with common electrochemical couples. Values are illustrative and rounded.
| Reaction Example | Cathode E° (V) | Anode E° (V) | n | E°cell (V) | ΔG° (kJ/mol) | K Approx. |
|---|---|---|---|---|---|---|
| Zn | Zn²⁺ || Cu²⁺ | Cu | 0.34 | -0.76 | 2 | 1.10 | -212.27 | 1.6 × 10^37 |
| Cu | Cu²⁺ || Ag⁺ | Ag | 0.80 | 0.34 | 2 | 0.46 | -88.77 | 3.9 × 10^15 |
| Fe | Fe²⁺ || Cu²⁺ | Cu | 0.34 | -0.44 | 2 | 0.78 | -150.52 | 2.2 × 10^26 |
| Br⁻ | Br₂ || Cl₂ | Cl⁻ | 1.36 | 1.07 | 2 | 0.29 | -55.96 | 6.5 × 10^9 |
Formula Used
E°cell = E°cathode − E°anode
ΔG° = −nFE°cell
ln(K) = nFE°cell / RT
log10(K) = nFE°cell / (2.303RT)
Where:
- n = electrons transferred in the balanced redox reaction
- F = Faraday constant, 96485.33212 C/mol
- R = gas constant, 8.314462618 J/mol·K
- T = absolute temperature in Kelvin
How to Use This Calculator
- Enter a clear reaction label or cell notation.
- Type the cathode half-cell name and its standard reduction potential.
- Type the anode half-cell name and its standard reduction potential.
- Enter the number of electrons transferred in the balanced overall reaction.
- Use 298.15 K for common standard-table comparisons, unless you want a different K estimate.
- Select the decimal precision for displayed results.
- Click the calculate button to show the result above the form.
- Use the CSV or PDF buttons to export the calculated report.
FAQs
1) What is standard potential?
Standard potential is the reduction voltage of a half-cell measured under standard-state conditions, usually 1 M, 1 bar, and 25°C. It indicates electron-accepting tendency.
2) Why does the calculator subtract anode potential from cathode potential?
Both entered values are reduction potentials. The cathode remains a reduction, while the anode is reversed to oxidation in the full cell. Subtraction gives the net driving voltage.
3) What does a positive E°cell mean?
A positive standard cell potential means the forward reaction is thermodynamically favorable under standard conditions. A negative value means the reverse reaction is favored instead.
4) What does ΔG° tell me?
ΔG° converts cell voltage into maximum useful electrical work per mole of reaction. More negative values indicate a stronger thermodynamic driving force for the written reaction.
5) Why can K become extremely large?
The equilibrium constant depends exponentially on cell potential. Even modest positive voltages can produce very large K values, especially when multiple electrons are transferred.
6) Can I enter oxidation potentials directly?
No. Enter reduction potentials from a standard electrochemical table. If your source provides an oxidation potential, reverse its sign before using it in this calculator.
7) Does temperature change the standard potential?
Standard potentials are commonly tabulated at standard conditions, usually 298.15 K. In this tool, temperature mainly affects the equilibrium constant estimate shown from your entered E°cell.
8) Does this tool handle nonstandard concentrations?
No. This page focuses on standard-state calculations. Real solutions may differ because of concentrations, activities, ionic strength, and other nonideal effects.