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Nernst Equation Calculator

Calculate non-standard cell potential E from E°, n, and Q, plus ΔG = −nFE.

Nernst equation calculator

Cell potential under non-standard conditions · ΔG = −nFE

E = E° − (0.05916/n) log₁₀ Q (25 °C)

E = 1.1 V

ΔG
-212.268 kJ/mol
ΔG°
-212.268 kJ/mol
T
298.15 K
  • Classroom form at 25 °C using 2.303RT/F ≈ 0.05916 V.

What is the Nernst Equation Calculator?

The Nernst equation gives the cell potential when concentrations (or pressures) are not standard: E = E° − (RT/nF) ln Q. At 25 °C textbooks often write E = E° − (0.05916/n) log₁₀ Q. The reaction quotient Q uses the same form as the equilibrium expression for the cell reaction.

Gibbs free energy relates to potential by ΔG = −nFE. The Nernst Equation Calculator returns E and the corresponding ΔG (and ΔG° from E°).

  • n = moles of electrons transferred in the balanced cell reaction
  • Q = 1 recovers E = E°
  • ΔG = −nFE (E in volts → ΔG in joules per mole of reaction)

Mathematical / chemical formulas

Forms used by the tool:

E = E° − (RT/nF) ln Q
E = E° − (0.05916/n) log₁₀ Q   (25 °C)
ΔG = −n F E

Step-by-step example: Non-standard Zn–Cu cell

E° = 1.10 V, n = 2, Q = 0.010 at 25 °C. Find E.

  1. E = 1.10 − (0.05916/2) log₁₀(0.010) = 1.10 − 0.02958(−2).
  2. E = 1.10 + 0.05916 ≈ 1.16 V.

Load the Zn–Cu Q = 0.010 preset and confirm E ≈ 1.16 V.

Frequently asked questions

What goes into Q?

Products over reactants with stoichiometric exponents, omitting pure solids and pure liquids, just as in K. Aqueous species use concentration (or activity); gases use partial pressure in bar in precise work.

Does a positive E mean the reaction is spontaneous?

For the cell reaction as written, E > 0 means ΔG < 0 under those conditions, so the forward cell reaction is spontaneous.

References & further reading

Standards bodies, university open courseware, and peer-reviewed references that align with the methods used on this page.

Keep learning with more calculators and study guides on Online Science Tools.

Practice problems & worked examples

Practice alongside the Nernst equation above. Each problem includes a full worked solution so you can check your reasoning step by step.

Practice problem 1

Standard conditions

E° = 1.10 V, n = 2, Q = 1. What is E at 25 °C?

Show solution

Worked solution

  1. log Q = 0 → E = E° = 1.10 V.

Answer: E = 1.10 V

Practice problem 2

Non-standard Q

E° = 1.10 V, n = 2, Q = 0.010 at 25 °C. Estimate E.

Show solution

Worked solution

  1. E = 1.10 − (0.05916/2) log(0.010) ≈ 1.10 + 0.059 ≈ 1.16 V.

Answer: E ≈ 1.16 V

Practice problem 3

Sign of ΔG

If E = +0.50 V and n = 2, is ΔG negative?

Show solution

Worked solution

  1. ΔG = −nFE < 0 when E > 0.

Answer: Yes, ΔG < 0

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