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Gibbs free energy calculator

Solve Gibbs free energy, enthalpy, entropy or temperature at constant pressure, and interpret the sign of the calculated free energy change.

Gibbs energy change (J/mol)
4,000.000000
Enthalpy change (J/mol)
10,000.000000
Entropy change (J/mol/K)
20.000000
Temperature
300
Thermodynamic interpretation
Reverse change is thermodynamically favoured

Estimates for information only. Not financial, medical, legal or engineering advice. See the Terms.

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How this calculator works

At constant temperature and pressure, subtract temperature times the entropy change from the enthalpy change. Use a consistent reaction basis and energy units: this page uses joules per mole and joules per mole per kelvin. A negative result favours forward change under the stated conditions but gives no reaction speed. If you enter standard enthalpy and entropy, the result is standard Gibbs energy; a nonstandard mixture also requires the RT ln(Q) correction.

Formula

DeltaG = DeltaH - T DeltaS; T = (DeltaH - DeltaG)/DeltaS.

Worked example

At 300 K, DeltaH = 10000 J/mol and DeltaS = 20 J/(mol K) give DeltaG = 4000 J/mol. With those same changes, DeltaG = 0 at 500 K if their temperature dependence is neglected.

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Frequently asked questions

Can entropy change be negative?

Yes. Signed enthalpy, entropy and Gibbs changes are accepted.

Can I use kJ for enthalpy and J for entropy?

Convert first: 1 kJ = 1000 J. Both energy quantities here are labelled in J.

Does negative Gibbs energy guarantee a quick reaction?

No. An activation barrier may still make the reaction very slow.

Sources

Written byAmira MansourCalculator writer. Builds and tests Mathulate calculators against published sources.
Reviewed byMarc LefebvreMathematics teacher. Checks each formula and worked example by hand.

Last updated .

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