Entropy Calculator
Enter the reversible heat transferred and the absolute temperature at which it occurs. The calculator returns the entropy change using ΔS = qrev / T, the standard relationship for a reversible process at constant temperature.
Last updated: September 26, 2026
Frequently asked questions
What is entropy change measuring here?
It measures the change in a system's entropy, a thermodynamic quantity related to the dispersal of energy, from the heat transferred reversibly at a constant absolute temperature.
Why must the process be reversible?
The relationship ΔS = qrev / T specifically uses the heat that would be transferred in a reversible (idealized, infinitely slow) process. Using the heat from an actual irreversible process in this formula gives an incorrect entropy change.
Why does the calculator require kelvin?
Absolute temperature is required because entropy is fundamentally tied to the thermodynamic (kelvin) temperature scale; Celsius has an arbitrary zero point that would make the ratio meaningless.
Does this work for processes where temperature changes?
Not directly. This formula assumes T stays constant during the heat transfer. Processes with changing temperature need an integral of dqrev/T over the process, which this simple calculator does not compute.
What does a positive or negative ΔS mean?
A positive ΔS means the system's entropy increased; a negative ΔS means it decreased. The sign depends on the direction and nature of the heat transfer you entered.
How does this relate to Gibbs Free Energy?
Entropy change is one of the three quantities (along with enthalpy change and temperature) used in ΔG = ΔH − TΔS on the Gibbs Free Energy Calculator to assess thermodynamic favorability.