# SLec12 - Lecture 12: Entropy We have found that entropy is...

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Lecture 12: Entropy We have found that entropy is a state variable (associated with equilibrium states of the system) and its change Δ S can be calculated along any reversible path. We have also obtained the Clausius inequality: It allows us to decide whether a process associated with the flow of heat δ q is irreversible and spontaneous , reversible or nonspontaneous. Example: Consider n moles of ideal gas isothermally expanded from V 0 to cV 0 . (dU=0= δ w+ δ q): If the initial and final states are the same, but the external pressure is fixed P=P 0 /c (irreversible and spontaneous process), we get

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We also have to consider the entropy change of the surroundings, Δ S surr . If the total entropy: the process is irreversible the process is reversible the process is nonspontaneous In the previous example, heat was taken isothermally and reversibly from the surroundings, so we get In the expansion against constant pressure (extraction of heat is almost reversible), we obtain Essentially, you can see that we study: system
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## This note was uploaded on 09/23/2010 for the course CHEM 342 taught by Professor Prestonsnee during the Spring '08 term at Ill. Chicago.

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SLec12 - Lecture 12: Entropy We have found that entropy is...

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