Calculator Inputs
This advanced tool combines the Nernst equation for redox cells with the electrochemical potential difference model for ion transfer between two states.
Example Data Table
These sample values illustrate how the calculator processes both cell voltage and ionic electrochemical potential contributions.
| Example | E° (V) | n | T (K) | Q | z | a₁ | a₂ | φ₁ (V) | φ₂ (V) | E (V) | ΔG (kJ/mol) | Δμ̃ (kJ/mol) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sample Run | 1.10 | 2 | 298.15 | 0.01 | 1 | 0.10 | 0.50 | 0.00 | 0.15 | 1.159159 | -223.683750 | 18.462527 |
| Near Standard State | 0.76 | 2 | 298.15 | 1.00 | 2 | 1.00 | 1.00 | 0.05 | 0.10 | 0.760000 | -146.657705 | 9.648533 |
Formula Used
1) Nernst Equation
E = E° − (RT / nF) ln(Q)
This adjusts the standard cell potential for actual reaction conditions. A smaller reaction quotient generally raises the potential for product-favored reactions.
2) Gibbs Free Energy Change
ΔG = −nFE and ΔG° = −nFE°
Negative Gibbs free energy indicates a thermodynamically spontaneous process at the entered conditions.
3) Equilibrium Constant
ln(K) = nFE° / RT
A larger equilibrium constant suggests products are strongly favored at equilibrium.
4) Electrochemical Potential Difference for Ion Transfer
Δμ̃ = RT ln(a₂ / a₁) + zF(φ₂ − φ₁)
The first term is the chemical contribution. The second term is the electrical contribution from moving a charged species between different electric potentials.
Symbols: R = gas constant, T = temperature, F = Faraday constant, n = electrons transferred, Q = reaction quotient, z = ion charge number.
How to Use This Calculator
- Enter the standard cell potential for the redox system.
- Provide the number of electrons transferred in the balanced reaction.
- Enter the temperature in Kelvin and the reaction quotient from current activities or concentrations.
- For ionic electrochemical potential, add the ion charge, both activities, and both phase potentials.
- Click the calculate button to show the results above the form.
- Review the computed voltage, Gibbs energy, equilibrium tendency, and electrochemical potential difference.
- Use the CSV and PDF buttons to export the current report.
FAQs
1) What does electrochemical potential mean here?
It combines chemical driving force and electrical driving force. In this page, the calculator reports both the redox cell potential and the ion transfer electrochemical potential difference.
2) Why must the reaction quotient be positive?
The Nernst equation uses the natural logarithm of Q. Logarithms require positive values, so zero or negative reaction quotients are physically and mathematically invalid.
3) What units should I use for temperature?
Always use Kelvin. Thermodynamic equations rely on absolute temperature, so Celsius or Fahrenheit values must be converted before entry.
4) What does a negative ΔG indicate?
A negative Gibbs free energy means the process is thermodynamically spontaneous under the entered conditions. A positive value means an external driving force would be required.
5) Why does the chart use log10(Q)?
Reaction quotients often span many orders of magnitude. A logarithmic horizontal scale shows the Nernst trend more clearly and keeps extreme values readable.
6) What are activities in the ion transfer equation?
Activities represent effective chemical availability rather than raw concentration alone. They better capture nonideal behavior, especially in concentrated or strongly interacting solutions.
7) Can the charge number be negative?
Yes. Negative ions have negative charge numbers, and that sign directly changes the electrical contribution term in the electrochemical potential difference calculation.
8) Why can the equilibrium constant be extremely large?
A strong positive standard potential can make products overwhelmingly favored. That pushes ln(K) very high, so the calculator may display K in power-of-ten form.