Entropy Calculator
Use this entropy calculator to estimate entropy change from thermodynamic data or simple ideal-gas expansion scenarios.
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Run the calculator.
What This Entropy Calculator Helps You Do
This page covers the three entropy calculations most people actually need: recover ΔS from Gibbs and enthalpy data, compute ΔS from reversible heat transfer, or estimate the entropy change of an ideal-gas volume change. That keeps the calculator useful across chemistry and thermodynamics coursework.
The result text calls out the sign of ΔS directly so you can move from the number to the physical interpretation without another step.
How to Calculate Entropy Calculator
- Choose the entropy workflow: Use Gibbs mode for thermodynamic reaction data, heat-transfer mode for reversible heating or cooling, or ideal-gas mode for isothermal expansion.
- Enter the required state variables: The calculator uses Kelvin internally and converts energy units where needed.
- Compute the entropy change: Each mode applies the matching thermodynamic equation and reports the sign and magnitude of ΔS.
- Interpret the sign: Positive entropy change indicates increasing disorder or accessible microstates, while negative entropy change indicates increasing order.
Entropy Calculator Formula
| Variable | Meaning | Unit |
|---|---|---|
| ΔS | Entropy change | J/mol·K or J/K |
| ΔH | Enthalpy change | kJ/mol |
| ΔG | Gibbs free energy change | kJ/mol |
| Qrev | Reversible heat transfer | J or kJ |
| T | Absolute temperature | K |
Use the worked examples below to check how the formula behaves with real values. If the result looks unexpected, verify the unit assumptions and the meaning of each variable before interpreting the answer.
Worked Examples
- ΔH: -92.0 kJ/mol
- ΔG: -32.0 kJ/mol
- T: 298 K
Result: ΔS is about -201.3 J/mol·K.
The reaction can still be spontaneous even with negative entropy if enthalpy is favorable enough.
- Qrev: 2.50 kJ
- T: 350 K
Result: ΔS is 7.14 J/K.
Adding reversible heat at constant temperature raises entropy.
- n: 1.0 mol
- V1: 1.0 L
- V2: 2.0 L
- T: 300 K
Result: ΔS is 5.76 J/mol·K.
Doubling the accessible volume increases the number of possible molecular arrangements.
- Qrev: -1.80 kJ
- T: 273 K
Result: ΔS is -6.59 J/K.
Removing heat reversibly lowers entropy.
How to Interpret Your Results
| Range | Meaning | Action |
|---|---|---|
| Negative ΔS | Entropy decreases. | Expect greater order, less accessible volume, or heat leaving the system. |
| ΔS near zero | Little entropy change. | Check whether the process is close to balanced or whether inputs were rounded. |
| Positive ΔS | Entropy increases. | Expect more disorder, more dispersal, or more accessible microstates. |
Frequently Asked Questions
References
Last reviewed: March 2026