Chemistry

Instant, private, and free

Gibbs Energy Calculator.

Calculate Gibbs free-energy change from enthalpy, absolute temperature, and entropy change.

On-device calculationNo signup
01

Set your values

Results update as you type.

Gibbs energy: -4,037 J/mol

Gibbs energy

-4,037.000000J/mol

Educational chemistry arithmetic only. Keep units consistent and verify assumptions against your laboratory or course specification.

Use Cases

Predict Reaction Spontaneity

Determine whether a chemical reaction is spontaneous under given conditions by calculating ΔG. Negative ΔG indicates a spontaneous process.

Example: For ΔH = -100 kJ/mol, T = 300 K, ΔS = 200 J/(mol·K), ΔG = -160 kJ/mol (spontaneous).

Evaluate Temperature Effects

Assess how changing temperature affects the spontaneity of a reaction, especially when ΔH and ΔS have opposite signs.

Example: For ΔH = +50 kJ/mol, ΔS = +100 J/(mol·K), reaction becomes spontaneous above 500 K.

Frequently Asked Questions

What is Gibbs free energy and why is it important?
Gibbs free energy (G) indicates the maximum reversible work a thermodynamic system can perform at constant temperature and pressure. Its change (ΔG) determines whether a reaction is spontaneous: negative ΔG means spontaneous, positive means non-spontaneous, and zero means equilibrium.
How is Gibbs free energy change calculated?
The calculator uses the equation ΔG = ΔH - TΔS, where ΔH is enthalpy change (J/mol), T is absolute temperature (K), and ΔS is entropy change (J/(mol·K)). Enter these values to get ΔG in J/mol.
What units should I use for the inputs?
Enter enthalpy change in J/mol, absolute temperature in Kelvin (K), and entropy change in J/(mol·K). The result will be in J/mol. Ensure temperature is in Kelvin, not Celsius, for correct calculations.

Tips & Common Mistakes

Tips

  • Ensure temperature is in Kelvin (K). Convert from Celsius by adding 273.15.
  • Double-check units: enthalpy in J/mol, entropy in J/(mol·K). If enthalpy is in kJ, convert to J by multiplying by 1000.
  • Remember that ΔG depends on temperature; a reaction may be spontaneous at one temperature but not another.
  • Use consistent units for all inputs to get the correct ΔG in J/mol.

Common Mistakes to Avoid

  • Using Celsius instead of Kelvin for temperature, leading to incorrect ΔG values.
  • Mixing units, e.g., entering enthalpy in kJ/mol while entropy is in J/(mol·K), without converting.
  • Forgetting that ΔG = 0 at equilibrium; interpreting a zero result as non-spontaneous instead of equilibrium.

Last updated: August 13, 2026