Chemistry Calculators

#1 Free Nernst Equation Calculator 2025

3 days ago
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Nernst Equation Calculator

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Calculation Result:

The Nernst equation relates the equilibrium cell potential (or electrode potential) of an electrochemical cell to its standard cell potential and the activities (often approximated by concentrations or partial pressures) of the reacting species.

It is crucial for understanding how cell potentials change under non-standard conditions (i.e., when concentrations are not 1 M, pressures are not 1 atm, or temperature is not 25°C/298.15K).

The equation allows us to predict the direction of spontaneous redox reactions and calculate the maximum electrical work a cell can perform under specific conditions.

The Nernst equation is given by:

E = E° - (RT / nF) * ln(Q)

Where:

  • E = Cell potential under non-standard conditions (in Volts)
  • E° = Standard cell potential (in Volts)
  • R = Ideal gas constant (8.314 J mol⁻¹ K⁻¹)
  • T = Temperature (in Kelvin, K)
  • n = Number of moles of electrons transferred in the balanced redox reaction
  • F = Faraday constant (96,485 C mol⁻¹)
  • ln(Q) = Natural logarithm of the reaction quotient Q

The Reaction Quotient (Q) for a general reaction aA + bB ⇌ cC + dD is:

Q = ([C]c * [D]d) / ([A]a * [B]b)

  • [X] represents the activity of species X. For dissolved solutes, this is often approximated by molar concentration (M). For gases, it's approximated by partial pressure (atm or bar).
  • Activities of pure solids, pure liquids, and solvents (like water in dilute solutions) are taken as 1 and are typically omitted from the Q expression.

Alternatively, using base-10 logarithm (log₁₀):

E = E° - (2.303 * RT / nF) * log₁₀(Q)

At a standard temperature of 25°C (298.15 K), the term (2.303 * RT / F) simplifies to approximately 0.0592 V:

E = E° - (0.0592 V / n) * log₁₀(Q)    (at 25°C / 298.15 K)

This calculator uses the general form with ln(Q) and allows variable temperature.

1. Enter Standard Conditions & Reaction Parameters:

  • Standard Cell Potential (E°): Enter the standard potential for the half-reaction or overall cell reaction in Volts.
  • Temperature (T): Enter the temperature at which the reaction occurs. Select the unit (°C or K). Default is 25°C.
  • Number of Electrons Transferred (n): Enter the total number of moles of electrons exchanged in the balanced redox reaction. This must be a positive integer.

2. Input Reaction Quotient (Q):

  • Select Q Input Method:
    • "Enter Q directly": If you have already calculated or know the value of Q, choose this and enter the numerical value.
    • "Calculate Q from species...": Choose this to input activities/concentrations and stoichiometric coefficients for individual products and reactants.
  • If Calculating Q from Species:
    • For each Product involved in the Q expression:
      • Click "Add Product Species".
      • Enter its activity (e.g., molar concentration for solutes, partial pressure in atm/bar for gases).
      • Enter its stoichiometric coefficient from the balanced chemical equation.
    • For each Reactant involved in the Q expression:
      • Click "Add Reactant Species".
      • Enter its activity.
      • Enter its stoichiometric coefficient.
    • Note: Pure solids, pure liquids, and the solvent (e.g., water in dilute solutions) have an activity of 1. You can either omit them from this input or enter an activity of 1 and a coefficient of 1.
    • Use the "-" button to remove a species row if added by mistake.

3. Calculate:

  • Click the "Calculate Cell Potential (E)" button.

4. View Results:

  • The calculated cell potential (E) under the specified non-standard conditions will be displayed.
  • The calculated or entered value of Q will also be shown.
  • A detailed step-by-step solution will illustrate how E was derived.
  • Error messages will appear for invalid inputs.

5. Reset:

  • Click the "Reset" button to clear all input fields and results.
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