Nernst Equation Calculator

Calculate the exact non-standard electrical potential of a galvanic cell based on temperature and reaction quotient (Q).

Standard Cell Potential (E°)

Temperature (T)

Moles of Electrons (n)

Reaction Quotient (Q)

Non-Standard Cell Potential (E)

1.1296 V

Nernst Correction Factor-0.0296 V

Reaction SpontaneitySpontaneous (Galvanic)

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Beyond Standard Conditions

In textbooks, galvanic cells (batteries) are always calculated under "Standard Conditions": exactly 1.0 Molar concentrations for all chemicals, 1 atm of pressure, and 25°C.

But what happens when you actually turn the battery on? As the battery powers your device, the reactants are consumed and the products build up. The concentrations are no longer 1.0 M, meaning the voltage physically drops. The Nernst Equation allows us to calculate the exact voltage of a battery under these real-world, non-standard conditions.

The Reaction Quotient (Q)

The key to the Nernst Equation is $Q$ , the Reaction Quotient. It is the mathematical ratio of the concentration of the products divided by the concentration of the reactants at any given moment.

When you buy a fresh battery, $Q$ is extremely tiny.
When the battery is dead, $Q$ is massive.

The Equation

\begin{aligned} E = E^\circ - \frac{RT}{nF} \ln(Q) \end{aligned}

Where:

Non-Standard Cell Potential

E^\circ

Standard Cell Potential

Ideal Gas Constant (8.314 J/mol·K)

Temperature (Kelvin)

Moles of Electrons Transferred

Faraday's Constant (96,485 C/mol)

Reaction Quotient

Interpreting the Results

If $Q < 1$ , the subtraction term becomes positive, and the real cell potential is higher than standard.
If $Q = 1$ (Standard conditions), the natural log of 1 is zero. The entire right side of the equation vanishes, leaving $E = E^\circ$ .
If the calculated $E$ ever hits exactly $0.00 V$ , the battery is completely dead (equilibrium has been reached).

Frequently Asked Questions

Faraday's Constant (96,485 Coulombs per mole) represents the total electrical charge carried by exactly one mole of electrons. It acts as the bridge linking chemical moles to physical electricity.

As the reactants turn into products, $Q$ gets larger. The natural log of $Q$ gets larger, meaning you subtract a larger and larger number from your Standard Potential ( $E^\circ$ ). Eventually, you subtract so much that the resulting voltage ( $E$ ) reaches 0.

If you assume the temperature is exactly 25°C (298.15 K), and you combine all the constants ( $R, T,$ and $F$ ) while converting the natural log (ln) to a base-10 log, the entire messy fraction mathematically simplifies to exactly $0.0592 / n$ .

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