Gibbs Free Energy Calculator (ΔG = ΔH − TΔS)
Compute the Gibbs free energy change of a reaction from its enthalpy, entropy and temperature to predict whether it is spontaneous.
kJ/mol
J/mol·K
K
Spontaneous
- 1
Convert ΔS to kJ/mol·K
−198,7 J/mol·K ÷ 1000 = −0,1987 - 2
T·ΔS product
298,15 K × −0,1987 kJ/mol·K = −59,242 - 3
Gibbs free energy ΔG = ΔH − T·ΔS
−92,2 − −59,242 = −32,958Negative ΔG means the reaction is spontaneous at this temperature.
Miten tämä laskin toimii?
Gibbs free energy change is ΔG = ΔH − T·ΔS. Convert ΔS from J/mol·K to kJ/mol·K, multiply by temperature in kelvin, and subtract from ΔH. A negative ΔG means the reaction is spontaneous, zero means equilibrium, and positive means non-spontaneous; the sign flips at T = ΔH/ΔS.
Kaava
How this is calculated
Enter the enthalpy change ΔH in kJ/mol, the entropy change ΔS in J/mol·K, and the absolute temperature T in kelvin. Because ΔH is in kilojoules but ΔS is conventionally tabulated in joules, the calculator divides ΔS by 1000 so both terms share kJ/mol units before subtracting.
The core relation is ΔG = ΔH − T·ΔS. A negative ΔG means the reaction is thermodynamically spontaneous (exergonic) at that temperature, ΔG = 0 means the system is at equilibrium, and a positive ΔG means the reaction is non-spontaneous (endergonic) as written and proceeds in reverse. The displayed status reflects the sign of ΔG.
When ΔH and ΔS have the same sign, spontaneity depends on temperature, and the reaction flips at the crossover (equilibrium) temperature T = ΔH/ΔS (kelvin). Below or above that point the sign of ΔG reverses. The calculator reports this temperature when it is physically meaningful (ΔS ≠ 0 and T ≥ 0). Temperatures must be non-negative on the Kelvin scale; values are treated as standard-state estimates assuming ΔH and ΔS are temperature-independent.
Usein kysytyt kysymykset
Standard enthalpies are tabulated in kJ/mol while standard entropies are in J/mol·K. Dividing ΔS by 1000 converts it to kJ/mol·K so the T·ΔS term matches ΔH and the subtraction is dimensionally consistent.
ΔG < 0 is spontaneous (the forward reaction is favored), ΔG = 0 is equilibrium, and ΔG > 0 is non-spontaneous as written. Spontaneity here is thermodynamic, not a statement about reaction rate.
When ΔH and ΔS share a sign, ΔG changes sign at T = ΔH/ΔS. This is the temperature at which the reaction switches between spontaneous and non-spontaneous, assuming ΔH and ΔS are roughly constant with temperature.
Tunnetaan myös nimellä
TG we-Calculate Editorial Team. (2026). Gibbs Free Energy Calculator (ΔG = ΔH − TΔS) [Online calculator]. TG we-Calculate. https://we-calculate.com/fi/calculator/gibbs-free-energy-calculator
TG we-Calculate Editorial Team. "Gibbs Free Energy Calculator (ΔG = ΔH − TΔS)." TG we-Calculate. 2026. https://we-calculate.com/fi/calculator/gibbs-free-energy-calculator.
TG we-Calculate Editorial Team, "Gibbs Free Energy Calculator (ΔG = ΔH − TΔS)," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/fi/calculator/gibbs-free-energy-calculator
@misc{wecalculate_gibbs_free_energy_calculator, title = {Gibbs Free Energy Calculator (ΔG = ΔH − TΔS)}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/fi/calculator/gibbs-free-energy-calculator}}, year = {2026}, note = {TG we-Calculate} }
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