Student Physics FAQ: Can Entropy Decrease Locally?…

Can Entropy Decrease Locally? How?

Yes. Entropy can decrease in a local, non-isolated system, provided that the entropy of its surroundings increases by at least as much. For a real irreversible process, the total entropy of the system and surroundings increases.

This is part of B.4 Thermodynamics, an HL-only IB Physics topic.

How Local Entropy Decrease Occurs

Entropy is a thermodynamic quantity related to the number of possible microscopic arrangements of a system. The second law of thermodynamics constrains the total entropy change of an isolated system:

\Delta S_{\text{total}}=\Delta S_{\text{system}}+\Delta S_{\text{surroundings}}\geq 0

Can Entropy Decrease Locally? How?

This is part of B.4 Thermodynamics, an HL-only IB Physics topic.

How Local Entropy Decrease Occurs

\Delta S_{\text{total}}=\Delta S_{\text{system}}+\Delta S_{\text{surroundings}}\geq 0

Process	Entropy condition
Reversible ideal process	$\Delta S_{\text{total}}=0$
Real irreversible process	$\Delta S_{\text{total}}>0$
Impossible spontaneous process	$\Delta S_{\text{total}}<0$

Can Entropy Decrease Locally? How?

How Local Entropy Decrease Occurs

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Can Entropy Decrease Locally? How?

How Local Entropy Decrease Occurs

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