Gibbs Free Energy Calculator
Gibbs free energy calculator (ΔG = ΔH − TΔS) — enter three of ΔG, ΔH, temperature and ΔS, solve for the fourth and see whether the reaction is spontaneous. Curriculum-aligned.
Gibbs Free Energy Calculator
Enter any three values and leave the fourth blank — the calculator solves for it. ΔG and ΔH are in kJ/mol, ΔS in J/(mol·K), temperature in K (or °C).
- Curriculum
- English (global) — Cambridge International + IB
- Built against
- Cambridge International A-Level Chemistry 9701 + IB Diploma (2023–2025) — Gibbs Free Energy
- Unit system
- SI primary; US/imperial readout below
- First published
- 2 Jun 2026
- Last updated
- 2 Jun 2026
View authoritative scientific sources
- Atkins, Physical Chemistry — Gibbs free energy
- CODATA 2018 — thermodynamic data
- BIPM SI Brochure, 9th edition (2019)
- Gibbs free energy — Encyclopædia Britannica
⚠️ Educational use only — see full disclaimer
EDUCATIONAL USE DISCLAIMER
This calculator is provided for educational and reference purposes only. It is not a substitute for instruction from a qualified teacher, your prescribed textbook, or your school's official curriculum materials.
When preparing for examinations, always cross-check our calculations and notation against your current syllabus and your teacher's guidance. Syllabus conventions and accepted notation vary between curricula and may change between examination years.
If you believe any calculation, notation, or curriculum reference in this tool is inaccurate, please let us know via the feedback button. We review feedback promptly and update tools when verified corrections are needed.
RECATOOLS accepts no liability for academic, examination, professional, or research outcomes arising from use of this tool.
How to Use the Gibbs Free Energy Calculator
Pick your curriculum
Use the curriculum pills above to match your syllabus (Cambridge A-Level/IB, 高考 or STPM). Terminology and the whole page follow your selection.
Enter three values
Type three of ΔG, ΔH, temperature and ΔS — leave the one you want to find blank. Watch out: ΔH is usually in kJ/mol but ΔS in J/(mol·K).
Read the result
The calculator solves for the blank quantity and tells you whether the reaction is spontaneous (ΔG < 0), at equilibrium, or non-spontaneous.
Check against your syllabus
The Tool Information block shows exactly which syllabus this is built against. Spot something off? Use the feedback button.
Gibbs Free Energy, in Your Curriculum's Words
Gibbs Free Energy (ΔG = ΔH − TΔS)
Example: A reaction has ΔH = −50 kJ/mol and ΔS = +100 J/(mol·K) at 298 K. Find ΔG and decide whether it is spontaneous.
Given: ΔH = −50 000 J/mol, T = 298 K, ΔS = 100 J/(mol·K). Using ΔG = ΔH − TΔS:
ΔG = −50 000 − (298 × 100) = −79 800 J/mol = −79.8 kJ/mol → spontaneous
Gibbs free energy combines enthalpy and entropy to predict whether a reaction happens spontaneously: ΔG = ΔH − TΔS. ΔH is the enthalpy change (heat), ΔS the entropy change (disorder), and T the absolute temperature in kelvin. If ΔG is negative the reaction is spontaneous at that temperature; if positive it is non-spontaneous; if zero the system is at equilibrium.
A common mistake is mixing units: ΔH and ΔG are usually given in kJ/mol, but ΔS in J/(mol·K) — a factor of 1000 apart. This calculator converts everything to consistent units for you. Because the TΔS term depends on temperature, some reactions switch from non-spontaneous to spontaneous when heated. All calculation happens in your browser — nothing is uploaded.
Gibbs free energy is the final arbiter of spontaneity — it combines energy and disorder into a single number.
10 Facts About Gibbs Free Energy
Gibbs free energy: ΔG = ΔH − TΔS.
ΔG < 0 means the reaction is spontaneous.
ΔG = 0 means the system is at equilibrium.
ΔH is usually in kJ/mol; ΔS in J/(mol·K).
The TΔS term depends on temperature.
Exothermic reactions have a negative ΔH.
Entropy measures the disorder of a system.
Some reactions are spontaneous only when heated.
Named after Josiah Willard Gibbs.
This calculator runs in your browser — your working stays private.
Frequently Asked Questions
- ΔG = ΔH − TΔS — the change in Gibbs free energy equals the enthalpy change minus the absolute temperature times the entropy change. The calculator can solve for any one of the four quantities when the other three are known, and also tells you the spontaneity of the reaction.
- If ΔG is negative, the reaction is spontaneous (it proceeds on its own) at that temperature. If positive, it is non-spontaneous and needs energy to drive it. If ΔG is exactly zero, the system is at equilibrium and no net change occurs.
- By convention ΔH and ΔG are given in kilojoules per mole (kJ/mol) because the values are large, while ΔS is given in joules per mole per kelvin (J/(mol·K)). This factor-of-1000 difference is a common source of error, so the calculator converts everything to consistent units before calculating.
- Because T in ΔG = ΔH − TΔS is an absolute temperature. Using degrees Celsius directly gives the wrong TΔS term. If you enter °C, the calculator converts it to kelvin by adding 273.15.
- Yes. Because the TΔS term depends on temperature, a reaction with both ΔH and ΔS positive becomes spontaneous only when the temperature is high enough, while one with both negative is spontaneous only at low temperatures.
- The chemistry — ΔG = ΔH − TΔS — is identical worldwide. What changes is the terminology; "Gibbs free energy" is 吉布斯自由能 in Chinese. The calculated value is the same.
- The Tool Information block lists the exact syllabus for your selected curriculum (e.g. STPM Kimia or Cambridge A-Level 9701). It is a study aid, not a substitute for your official syllabus or teacher.
- No. Every calculation runs in your browser; nothing you type is uploaded. It works offline once the page has loaded.
- Completely free, no account or usage limit. It runs entirely in your browser and collects no data.
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