Entropy Change Calculator
entropy change calculator. Get instant, accurate results. Enter values for instant results with step-by-step formulas.
Reviewed for accuracy by Manoj Kumar, Mathematics Educator
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Formula: ΔS = Q/T (isothermal) | ΔS = nCₚln(T₂/T₁) (isobaric)
Worked example — 3.33 J/K
ΔS = Q/T (isothermal) | ΔS = nCₚln(T₂/T₁) (isobaric)
Entropy measures disorder. Second law: total entropy of isolated system always increases.
Problem:Q=1000 J at T=300 K
Solution:ΔS=1000/300=3.33 J/K
Result:3.33 J/K
Entropy change (ΔS) measures the change in disorder or randomness of a system. For a reversible isothermal process, ΔS = Q/T, where Q is heat transferred in joules (J) and T is the absolute temperature in kelvin (K). The SI unit of entropy is J/K (joules per kelvin).
For an isothermal process, use ΔS = Q/T. If 1000 J of heat flows into a system at 300 K: ΔS = 1000 / 300 ≈ 3.33 J/K. For an isobaric process with n moles of an ideal gas, ΔS = nCₚ ln(T₂/T₁). A positive ΔS means heat flows in; negative means heat flows out.
Heat transfer Q is entered in joules (J) — use positive values for heat absorbed and negative for heat released. Temperature T must be in kelvin (K), not Celsius; convert with T(K) = T(°C) + 273.15. The output ΔS is in J/K (joules per kelvin), the standard SI unit for entropy.
Locally, yes — a refrigerator decreases entropy inside the food compartment by removing ~200 J/K of entropy per hour. But it dumps more entropy into the room, making the total entropy of the refrigerator-plus-room system increase, in full compliance with the Second Law of Thermodynamics.
Reviewed for accuracy by Manoj Kumar, Mathematics Educator · Editorial policy
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