Free · Chemical thermodynamics calculators 🌡️

Reaction and Ideal-Gas Entropy Relations

Combine reaction entropies, Gibbs energy and reversible isothermal ideal-gas volume or pressure changes.

  • Formula & worked example
  • Private in your browser
  • No signup
Go to tool

Calculator inputs

Loading calculator…

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.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

Enthalpy 1000 J, temperature 26.85 °C (300 K) and entropy change 2 J/K give Gibbs energy 400 J.

Delta G = Delta H − T Delta S; ideal-gas Delta S = nR ln(V2/V1)

Worked example

Enter these known values and leave the other values blank.

Change in enthalpy
1000 J
Temperature
26.85 °C
Change in entropy
2 J /K
Change in Gibbs free energy
400 J

Assumptions and limitations

  • Reaction standard molar entropies must already include their stoichiometric weighting and matching reference state. The Gibbs relation requires absolute temperature and consistently scaled enthalpy and entropy.
  • Gas branches describe reversible isothermal ideal-gas changes. A negative Delta G classifies thermodynamic favorability at the specified conditions, not reaction speed or a safety decision. The captured gas constant is rounded to 8.3145 J/(mol K).

Common questions

What does this model assume?

Reaction standard molar entropies must already include their stoichiometric weighting and matching reference state. The Gibbs relation requires absolute temperature and consistently scaled enthalpy and entropy.

Can I solve backward?

Clear the unknown value and enter compatible known values. Choices, one-way outputs and singular boundary cases cannot always be inverted.

References

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

Explore chemical thermodynamics calculators 🌡️ or browse all chemistry calculators.