Gibbs Free Energy Calculator

Gibbs Free Energy Calculator

Compute ΔG = ΔH − TΔS (ensure consistent units: ΔH in kJ/mol, ΔS in J/mol·K).

2026-05-06T10:07:27.216Z
kJ/mol
K
J/(mol·K)

Gibbs Free Energy (ΔG)

0.0000 kJ/mol

0.00 J/mol

Formula: ΔG = ΔH − TΔS

Reaction at Equilibrium

What is Gibbs Free Energy?

Gibbs free energy (G) is a thermodynamic potential that indicates the maximum reversible work obtainable from a process at constant temperature and pressure. ΔG helps predict whether a process is thermodynamically favourable under given conditions.

Note: ΔG addresses thermodynamic spontaneity, not kinetics. A negative ΔG means the reaction is energetically favourable, but it may still be slow without a suitable pathway or catalyst.

How to Use

  1. Enter ΔH in kJ/mol (reaction enthalpy).
  2. Enter temperature in kelvin (K).
  3. Enter ΔS in J/(mol·K); the tool converts ΔS to kJ/(mol·K) internally.
  4. Read ΔG in kJ/mol and J/mol and the spontaneity hint.
  5. Remember to use temperature-specific ΔH and ΔS when available.

Worked Example

Given: ΔH = -100 kJ/mol, ΔS = -50 J/(mol·K), T = 298.15 K
Step: ΔG = -100 − (298.15 × (-50 / 1000)) = -85.0925 kJ/mol
Result: -85.0925 kJ/mol

Frequently Asked Questions

What is ΔG?

ΔG is Gibbs free energy change; negative values indicate spontaneous (exergonic) processes at constant T and P.

Units used?

ΔH in kJ/mol, ΔS in J/(mol·K), ΔG returned in kJ/mol and J/mol.

Why convert ΔS?

ΔS provided in J/(mol·K) is converted to kJ/(mol·K) by dividing by 1000 to match ΔH units.

What if T ≤ 0?

Temperature must be positive (kelvin). Use absolute temperature.

Is ΔG the only criterion?

ΔG indicates thermodynamic favorability, not reaction rate — kinetics and activation energy matter too.

Can ΔG change with T?

Yes — ΔG depends on temperature; use temperature-specific ΔH and ΔS when available.

What does zero ΔG mean?

ΔG = 0 indicates the system is at equilibrium under the given T and P.

Any cautions?

This is a calculator for idealized thermodynamic math; consult literature for empirical values.

Formula: ΔG = ΔH − TΔS. ΔH (kJ/mol), ΔS (J/mol·K) converted to kJ/(mol·K) internally.

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