Equilibrium Constant from Gibbs Energy Calculator

How it is calculated

Enter ΔG in kJ/mol and the temperature in kelvin. The tool converts ΔG to joules and uses ln K = −ΔG ÷ (R × T) with R = 8.314 J/(mol·K), then K = eln K. Temperature must be above zero. K is shown to four decimals, but values below 0.0001 or at 1,000,000 and above switch to scientific notation such as 1.0188 × 10⁷. If the answer is too large for the computer to represent (an absurd ΔG such as −20000 kJ/mol), no result is shown. The spontaneity line only follows the sign of the ΔG you typed: negative is Spontaneous, positive is Non-spontaneous, exactly zero is At equilibrium. For K to be the usual equilibrium constant, ΔG should be the standard free energy change ΔG° at that temperature, and the K here is dimensionless.

Common mistakes

• Entering ΔG in joules instead of kJ/mol. A value of −20000 is read as −20,000 kJ, the exponential overflows and the tool shows no result; divide joules by 1000.
• Entering the temperature in °C. Use kelvin: 25 °C is 298.15, not 25. With 25 the tool returns 6.1549 × 10⁴¹, which is nonsense but is displayed, and 0 or a negative temperature gives no result.
• Using ΔG at nonstandard conditions (with the reaction quotient Q) and expecting K. The relation K = e^−ΔG°/RT needs the standard free energy change; the actual ΔG changes as the reaction proceeds.
• Confusing the sign: a negative ΔG gives K above 1, a positive ΔG gives K below 1. Reading the label Non-spontaneous as "never occurs" ignores that K = 0.0024 still means a small amount of product forms.
• Assuming ΔG is constant with temperature. The ΔG must be the value at the temperature you enter; reusing a 25 °C value at 100 °C gives the wrong K.