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I don't really understand the basic principles behind this and so I am looking for a good explanation on it.

My lecture notes use inequalities like $dS \geq 0$, yet in a question involving calculating the entropy change when compressing Argon, the total entropy change was negative.

Then there is the notion entropy change of the system and entropy change of the surroundings? Can any of these be negative?

In other words, when can entropy be negative? In what circumstances is it strictly positive?

Qmechanic
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PhysicsMathsLove
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1 Answers1

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Basic answers about entropy and its definition can be found elsewhere on this site, so we refrain from providing them here again.

For a closed system undergoing an irreversible process the entropy in the final state must always be greater or equal than the entropy in the initial state. This, however, does not pose any limitation on the value of the entropy for any system at any given state, process and time. In particular non-isolated system need not fulfill the above and isolated system may present negative entropy as long as the final variation after irreversible processes is positive.

gented
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