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Nernst Equation Calculator

Find a cell potential away from standard conditions.

How it is calculated

The Nernst equation corrects a standard cell potential for non-standard concentrations: E = E° − (R·T ÷ (n·F)) × ln Q. E° is the standard potential in volts, n the number of electrons transferred, Q the reaction quotient (products over reactants, each raised to its coefficient), T the temperature in kelvin (the tool converts from °C by adding 273.15, and assumes 25 °C if blank), R = 8.314462618 J/(mol·K) and F = 96485.332 C/mol. The tool shows the corrected potential and the correction term, both in volts with four decimals. n and Q must be above zero.

Worked example

Daniell-type cell: E° = 1.10 V, n = 2, Q = 10, 25 °C so T = 298.15 K. R·T ÷ (n·F) = 8.314462618 × 298.15 ÷ (2 × 96485.332) = 0.01285 V. ln 10 = 2.3026, so the correction term = 0.01285 × 2.3026 = 0.0296 V. E = 1.10 − 0.0296 = 1.0704 V.

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Common mistakes

  • Entering the temperature in kelvin; the field is in °C and 298 would add 273 again.
  • Putting reactants over products in Q, which flips the sign of the correction.
  • Including pure solids and liquids in Q; their activity is 1 and they are left out.
  • Using the wrong n; it is the electrons in the balanced overall reaction, not the charge of a single ion.
  • Using Q = 0 or a negative number; the logarithm is not defined and the tool returns nothing.

About this calculator

This calculator finds a cell or electrode potential away from standard conditions using the Nernst equation: E = E° − (RT / nF) ln(Q), which at 25°C simplifies to E = E° − (0.0592/n) log(Q), where E° is the standard potential, n is the moles of electrons transferred, F is Faraday's constant, and Q is the reaction quotient.

Electrochemistry and general chemistry students, and engineers designing batteries, fuel cells, or corrosion-monitoring systems, use it whenever concentrations or temperatures differ from standard state, since real electrochemical cells rarely operate at 1 M concentrations and 25°C.

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Comments (1)

  • Editorial team

    Build Q from concentrations in mol/L for dissolved species and pressures in bar or atm for gases, and leave pure solids and liquids out. A useful limit to know: when the corrected potential falls to zero, Q has reached the equilibrium constant and the cell is flat. With E° = 1.10 V and n = 2 that happens near Q = 1e37. Which cell or electrode reaction are you working on?

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