What units should I use for ΔH and ΔS?

Enter ΔH in kJ/mol and ΔS in J/mol·K. The calculator automatically divides ΔS by 1000 before multiplying by T so both terms are in kJ/mol when computing ΔG.

What does a negative ΔG mean?

A negative ΔG (ΔG < 0) means the reaction is thermodynamically spontaneous under the given conditions — it can proceed without continuous energy input, though it says nothing about reaction rate.

What does a positive ΔG mean?

A positive ΔG (ΔG > 0) means the reaction is non-spontaneous in the forward direction. It will not proceed on its own; energy must be supplied (for example, via coupling with an ATP hydrolysis step in biology).

Can I enter temperature in Celsius?

Yes. Switch the temperature unit selector to Celsius and the tool converts your input to Kelvin (K = °C + 273.15) before calculating. The result is always displayed in Kelvin for clarity.

What is the crossover temperature?

When ΔH and ΔS have the same sign, there is a temperature T = ΔH / ΔS at which ΔG = 0 (equilibrium). The tool displays this crossover temperature when applicable.

Does ΔG = 0 mean the reaction does not occur?

No. ΔG = 0 means the system is at equilibrium — both the forward and reverse reactions occur at equal rates, so there is no net change in composition.

Gibbs Free Energy Calculator

Name: Gibbs Free Energy Calculator
Availability: InStock
Author: Nham Vu

Enter enthalpy change, temperature, and entropy change to calculate Gibbs free energy and determine reaction spontaneity.

Inputs

ΔG = ΔH − T·ΔS

Enthalpy Change (ΔH)

kJ/mol

Temperature (T)

Entropy Change (ΔS)

J/mol·K

Enter values on the left and click Calculate to see the result.

Copied!

Summary

Enter enthalpy change, temperature, and entropy change to calculate Gibbs free energy and determine reaction spontaneity.

How it works

Enter the enthalpy change (ΔH) in kilojoules per mole (kJ/mol).
Enter the temperature in Kelvin (K) or switch to Celsius — the tool converts automatically.
Enter the entropy change (ΔS) in joules per mole per Kelvin (J/mol·K).
Click Calculate; the tool applies ΔG = ΔH − TΔS (converting ΔS from J to kJ internally).
Review the result: sign, magnitude, spontaneity verdict, and a plain-language explanation.
Use the Reset button to clear all fields and start a new calculation.

Use cases

Determine whether a chemical reaction will proceed spontaneously under given conditions.
Solve thermodynamics problems in general chemistry and physical chemistry courses.
Find the crossover temperature at which a reaction switches from spontaneous to non-spontaneous.
Verify hand-calculated ΔG values for lab reports or homework assignments.
Analyze industrial reactions to predict feasibility without running the experiment.
Study the interplay between enthalpy and entropy in driving chemical processes.
Prepare for AP Chemistry, university thermodynamics, or graduate-level physical chemistry exams.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu