For heat ΔQ transferred, the entropy of region 1 decreases according to ΔS1=−ΔQ/T1, while the entropy of region 2 increases by \(\...For heat ΔQ transferred, the entropy of region 1 decreases according to ΔS1=−ΔQ/T1, while the entropy of region 2 increases by ΔS2=ΔQ/T2. In the idealized limit of very small, but nonzero temperature difference, the flow of heat is said to be reversible because the generation of entropy is negligible.
