Entropy change of system in adiabatic irreversible process [duplicate]








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[Formula of entropy change](/questions/24518/formula-of-entropy-change)

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In an adiabatic irreversible process we know that q = 0. Now change in entropy is defined as q/T. So when q is zero, why is change in entropy not zero ?




The change in entropy is the *reversible* heat flow divided by $T$. So if the process is irreversible, you can't use the irreversible process's heat flow to find the entropy change.


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