HesapHanem

Equilibrium Constant Calculator

Find the equilibrium constant from ΔG.

How it is calculated

The engine applies K = exp(−ΔG / (R·T)) with R fixed at 8.314 J/(mol·K). Because R is in joules, ΔG must be entered in J/mol (not kJ/mol), and T in kelvin. The temperature has to be greater than zero, otherwise there is no result; any ΔG, positive, negative or zero, is accepted. K is shown to four decimals and has no unit; a K below 0.01 or at 1,000,000 and above is shown in scientific notation instead (ΔG = 30000 J/mol at 298.15 K gives 5.5454 × 10⁻⁶). ΔG = 0 gives K = 1, negative ΔG gives K above 1, positive ΔG gives K below 1. It treats ΔG as the standard value ΔG°; for a mixture away from standard state use the reaction quotient instead.

Worked example

Take ΔG = −10000 J/mol (that is −10 kJ/mol) at T = 298.15 K (25 °C). Step 1: R·T = 8.314 × 298.15 ≈ 2478.8 J/mol. Step 2: −ΔG / (R·T) = 10000 / 2478.8 ≈ 4.0342. Step 3: K = exp(4.0342). The result is 56.4965, so products are strongly favoured at equilibrium.

Try this example →

Common mistakes

  • Entering ΔG in kJ/mol: typing −30 instead of −30000 gives K = 1.0122 instead of a value near 180,000.
  • Using Celsius for temperature; 25 must be entered as 298.15 K.
  • Flipping the sign of ΔG: a negative ΔG gives K above 1, so −10000 and +10000 give very different answers.
  • Using the value for a reaction not at standard conditions; the formula assumes the standard free energy change ΔG°.

About this calculator

This calculator finds the equilibrium constant K of a chemical reaction from its Gibbs free energy change using K = exp(−ΔG°/RT), the rearranged form of the thermodynamic relation ΔG° = −RT·ln(K), where R is the gas constant (8.314 J/mol·K) and T is the absolute temperature. This equation is the bridge between thermodynamics and chemical equilibrium: a large negative ΔG° (a thermodynamically favorable reaction) produces a K much greater than 1, meaning the equilibrium lies far toward products, while a positive ΔG° gives K less than 1, favoring reactants.

Chemistry students and researchers use this to connect free-energy data from tables to predicted reaction extent; chemical engineers use it when designing reactors to predict how far a reaction will proceed under given conditions; and biochemists use the same relationship to study equilibria in enzyme reactions, ligand binding, and protein folding.

Was this helpful?

You can pick up to 3 reactions.

Comments (1)

  • Editorial team

    A handy sanity check: at 298 K, every 5.7 kJ/mol in the standard free energy shifts K by a factor of about ten. So entering minus 5708 J/mol should give a K near 10. A K below 0.01 prints in scientific notation, so a ΔG of 30000 J/mol at 298.15 K shows 5.5454 × 10⁻⁶ rather than a rounded zero. What reaction and temperature are you checking?

Popular calculators

Loan Calculator

Monthly payment, total interest and full amortization schedule.

Percentage Calculator

Percent change, percent of, and ratio calculations.

Discount Calculator

Calculate final price, savings, and discount amount.

BMI Calculator

Body mass index from height and weight (metric or imperial).

Age Calculator

Compute your exact age in years, months and days from a birth date.

Compound Interest Calculator

Calculate the final amount and interest earned with compounding.

All Calculators