Gibbs Free Energy Calculator
A reaction with ΔH = −200 kJ/mol and ΔS = −100 J/(mol·K) has ΔG = -100 kJ/mol at 1000 K, so it is spontaneous; above 2000 K it reverses.
-100 kJ/mol
- Reaction is
- spontaneous (ΔG < 0)
- Equilibrium constant K = e^(−ΔG/RT)
- 167248.4156
- log₁₀ K
- 5.223362012
- Temperature where ΔG = 0 (ΔH/ΔS)
- 2000 K
Step-by-step solution
- ΔG = ΔH − TΔS = -200 kJ/mol − 1000 K × -100 J/(mol·K)
- ΔG = -100 kJ/mol
- K = exp(−ΔG/RT) = exp(12.0272355) = 167248.4156
Gibbs Free Energy Formula
ΔG = ΔH − TΔS, K = exp(−ΔG/RT)
R = 8.314 J/(mol·K); ΔG = 0 at T = ΔH/ΔS
Worked Example
A reaction with ΔH = −200 kJ/mol and ΔS = −100 J/(mol·K) at 1000 K:
- ΔG = ΔH − TΔS = -200 kJ/mol − 1000 K × -100 J/(mol·K)
- ΔG = -100 kJ/mol
- K = exp(−ΔG/RT) = exp(12.0272355) = 167248.4156
Equilibrium constant K = e^(−ΔG/RT): 167248.4156 · log₁₀ K: 5.223362012 · Temperature where ΔG = 0 (ΔH/ΔS): 2000 K
GATE tip
Watch the units: ΔH is usually in kJ and ΔS in J. Mixing them is the commonest slip in Ellingham-type questions.
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Frequently asked questions
How does this relate to the Ellingham diagram?
An Ellingham line plots ΔG° = ΔH° − TΔS° per mole of O₂ against T: the slope is −ΔS° and the intercept ΔH°. Lower lines mean more stable oxides.
What does a large K mean?
K ≫ 1 means products dominate at equilibrium; every 5.7 kJ/mol more negative ΔG at 298 K multiplies K by 10.
Sources
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
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APA
Scientific Converters. (2026, October 15). Gibbs Free Energy Calculator. Retrieved October 25, 2026, from https://scientificconverters.com/calculators/gibbs-free-energy-calculator/
IEEE
Scientific Converters, "Gibbs Free Energy Calculator," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/calculators/gibbs-free-energy-calculator/