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Gibbs Energy from Enthalpy, Entropy & Temperature

Relate Gibbs energy change, enthalpy change, entropy change and absolute temperature on a common process basis.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

At 300 K, enthalpy change 10 kJ and entropy change 0.02 kJ/K give Gibbs energy change 4 kJ: 10 − 300 × 0.02.

ΔG = ΔH − TΔS, with absolute temperature T in kelvins

Worked example

Enter these known values and leave the other values blank.

Enthalpy change for the process
10 kJ
Entropy change for the same process
0.02 kJ /K
Process temperature
300 K
Gibbs energy change
4 kJ

Assumptions and limitations

  • Absolute temperature must be positive. Enthalpy and entropy changes must refer to the same process, material amount and temperature.
  • Entropy units are energy per kelvin. For example, 20 J/K equals 0.02 kJ/K; temperature selectors convert to kelvins for the product TΔS.
  • At constant temperature and pressure, negative ΔG indicates a thermodynamically favorable direction for the specified change. It does not predict reaction speed.
  • Calorie units are thermochemical: exactly 4.184 J per calorie. If entropy change is zero, ΔG equals ΔH and those two values cannot uniquely determine temperature.

Common questions

Does a negative result mean the reaction is fast?

No. Thermodynamic favorability and reaction rate are different questions. Kinetic barriers can make a favorable process very slow.

Can I combine kJ for enthalpy with J/K for entropy?

Yes. Select the appropriate unit for each field. The calculator converts them before multiplying entropy by absolute temperature.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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