About the Entropy Change Calculator
What is the Entropy Change Calculator?
Entropy measures how spread out energy is. This entropy change calculator covers the three textbook cases: heating a substance, a phase change at constant temperature, and an ideal gas expanding at constant temperature.
A positive ΔS means energy has become more dispersed.
How to use the Entropy Change Calculator
- Process (sample: Heating or cooling (m c ln T₂/T₁))
- Mass (kg) (sample: 1)
- Specific Heat (J/kg·K) (sample: 4,186)
- Initial Temperature (°C) (sample: 20)
- Final Temperature (°C) – also the phase-change temperature (sample: 80)
- Latent Heat (J/kg) (sample: 3,34,000)
- Moles of Gas (sample: 1)
- Volume Ratio V₂ ÷ V₁ (sample: 2)
- Press Calculate Entropy Change (results also refresh as you type). The result card shows the Entropy Change, along with In kJ/K and Direction.
Formula used
Heating: ΔS = m c ln(T₂ ÷ T₁); Phase change: ΔS = m L ÷ T; Gas: ΔS = n R ln(V₂ ÷ V₁)
- T = absolute temperature in kelvin
- L = latent heat (ice melting 334 kJ/kg, water boiling 2,257 kJ/kg)
The total entropy of an isolated system never decreases (second law of thermodynamics).
Worked example
These are the sample values already filled in the calculator above, and the result it returns for them:
| Input | Sample value |
|---|---|
| Process | Heating or cooling (m c ln T₂/T₁) |
| Mass (kg) | 1 |
| Specific Heat (J/kg·K) | 4,186 |
| Initial Temperature (°C) | 20 |
| Final Temperature (°C) – also the phase-change temperature | 80 |
| Latent Heat (J/kg) | 3,34,000 |
| Moles of Gas | 1 |
| Volume Ratio V₂ ÷ V₁ | 2 |
| Result | Value |
|---|---|
| Entropy Change | 779.469 J/K |
| In kJ/K | 0.77947 kJ/K |
| Direction | Entropy increases (more disorder) |
Tips for using the Entropy Change Calculator
- Boiling increases entropy far more than melting, because gases are much more disordered.
- Use kelvin for all temperatures; the calculator converts from °C for you.