For a reversible process, the source defines the change in entropy ΔS using heat transfer Q and absolute temperature T. What is this definition, and in what SI unit is entropy measured?
AΔS = Q x T, measured in joules
BΔS = Q/T, measured in joules per kelvin
CΔS = T/Q, measured in kelvins per joule
DΔS = Q - T, measured in joules per kelvin
Answer & Solution
Correct answer: B. ΔS = Q/T, measured in joules per kelvin
1. The source defines the entropy change for a reversible process as the ratio of heat transfer to the absolute temperature at which it occurs, ΔS = Q/T.
2. Since Q is measured in joules and T is measured in kelvins, this ratio naturally comes out in joules per kelvin.
3. This unit is stated directly: the SI unit for entropy is joules per kelvin.
4. Option C inverts the ratio to T/Q, and options A and D replace division with multiplication or subtraction, neither of which matches the stated definition.
_Source: OpenStax College Physics (CC BY 4.0), Ch 15 "Thermodynamics", section 15.6 Entropy and the Second Law of Thermodynamics: Disorder and the Unavailability of Energy_
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