Chemistry Calculator
Nernst Equation Calculator (Cell Potential Calculator)
The Nernst equation converts standard cell potential (E°) into real-world cell potential (E) by accounting for temperature and how far the reaction has progressed (Q). Use this calculator to estimate cell voltage under non-standard conditions.
Nernst Equation
Calculate cell potential from E°, T, n, and Q
Results
Enter values to calculate E
What is the Nernst equation?
In electrochemistry, standard potentials (E°) are defined for idealized conditions (typically 1 M solutions, 1 bar gases, pure solids/liquids, and 25°C). Real cells almost never operate exactly at those conditions.
The Nernst equation adjusts E° using the reaction quotient Q, which summarizes the current ratio of products to reactants. As Q increases, the driving force typically decreases, reducing cell potential.
Nernst equation formula
Natural log form:
E = E° − (RT / nF) · ln(Q)
Base-10 form (equivalent):
E = E° − (2.303RT / nF) · log10(Q)
Where R is the gas constant, F is Faraday’s constant, n is electrons transferred, T is temperature in kelvin, and Q is the reaction quotient.
How to use the calculator
- Enter E° (standard cell potential) from a table or your half-cell data.
- Set temperature in °C (the calculator converts to kelvin internally).
- Enter n (electrons transferred) from the balanced redox reaction.
- Enter Q from your current concentrations/activities and stoichiometry.
- Choose log10(Q) if you want the common textbook form at 25°C.
Example calculations
These examples show how Q and temperature shift E relative to E°.
Example 1 — Room temperature, Q = 10
E° = 1.10 V, T = 25°C, n = 2, Q = 10
At 25°C: E = E° − (0.05916/n) · log10(Q)
E = 1.10 − (0.05916/2) · log10(10)
E = 1.10 − 0.02958 · 1 = 1.07042 V
Example 2 — Products low (Q < 1)
E° = 0.80 V, T = 25°C, n = 2, Q = 0.01
log10(0.01) = −2
E = 0.80 − (0.05916/2) · (−2)
E = 0.80 + 0.05916 = 0.85916 V
Example 3 — Higher temperature increases the correction
E° = 1.23 V, T = 60°C, n = 2, Q = 100
Higher T increases (RT/nF), so the |correction| grows
For Q = 100, log10(Q) = 2
E will be lower than E° by a larger amount than at 25°C
Frequently Asked Questions
- What does the Nernst equation calculate?
- It calculates the cell potential (E) under non-standard conditions by correcting the standard potential (E°) using temperature, electron transfer (n), and the reaction quotient (Q).
- What is the reaction quotient Q?
- Q is the ratio of products to reactants (raised to stoichiometric powers) using activities or effective concentrations. Q must be positive and dimensionless.
- What does n mean in the Nernst equation?
- n is the number of electrons transferred in the balanced redox reaction. It controls how strongly E changes with Q and temperature.
- Why is 25°C often special in electrochemistry?
- At 25°C (298.15 K), the Nernst equation is often written in base-10 form: E = E° − (0.05916/n) log10(Q). This is just a convenient constant for room temperature.