Gibbs Free Energy Calculator

Relate enthalpy, entropy, and temperature to determine free energy changes and predict reaction spontaneity.

DeltaH (kJ/mol)

Negative enthalpy indicates an exothermic reaction.

DeltaS (J/(mol K))

Include the sign for entropy change.

Temperature (K)

Use absolute temperature in Kelvin.

Gibbs free energy change

-4.24 kJ/mol

Spontaneous under the given conditions.

Approximate equilibrium constant K: 5.536

How to Use This Calculator

Obtain enthalpy and entropy changes from tables or experiments, keeping track of units.

Choose the Kelvin temperature of interest. DeltaG depends on operating temperature.

The calculator converts entropy to kJ and applies DeltaG = DeltaH - T * DeltaS.

Negative DeltaG means the process is spontaneous as written; positive means non-spontaneous.

DeltaG = DeltaH - T * DeltaS

Use DeltaH in kJ/mol, DeltaS in J/(mol K), and temperature in Kelvin. To compute K, use K = exp(-DeltaG / (R T)) with R in kJ units.

Example

With DeltaH = -40 kJ/mol, DeltaS = -120 J/(mol K), and T = 298 K: DeltaG = -40 - 298 * (-0.120) = -4.24 kJ/mol.

Gibbs free energy connects enthalpy and entropy to predict whether a process proceeds spontaneously at constant temperature and pressure.

This calculator helps evaluate temperature dependence, compare reactions, and estimate equilibrium constants using standard thermodynamic data.

Entropy tables typically use J/(mol K). The calculator converts to kJ to match DeltaH units.

Yes. Adjust temperature and observe when DeltaG changes sign to estimate crossover points.

The calculator reports K when DeltaG and temperature are finite, using the relation K = exp(-DeltaG/(R T)).

At constant pressure, Gibbs free energy predicts spontaneity. For varying pressure, use chemical potentials or activities.

The process is non-spontaneous as written. It may become spontaneous at higher temperature or in the reverse direction.