Lecture 37 - Lecture 37 pls-37.1 Entropy and the 2nd Law of...

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Lecture 37 pls-37.1 Entropy and the 2 nd Law of Thermodynamics Media: 1. Fan w/ hot, cold water and LN 2 2. Figs. 1, 2 1. S and The entropy S is a function of the thermodynamic state of the system, similar to the internal energy U and pressure P . E.g., for an IMG, if we know N , V , and T , we know T Nk U B 2 3 = and T k V N P B = Similarly, = C N V N U Nk S B 2 3 ln For a system at temperature T , if we add a small amount of heat Q , then the change in entropy of the system is T Q S = Remember, Q is not a state function, but the entropy S is. Relationship to PV diagram ( Fig. 1 ): (i) On an adiabat 0 = Q Æ 0 = S Æ S is constant along an adiabat. That is, an adiabat is a constant entropy curve. ( C is a constant that depends upon the mass of the atoms in the gas)
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Lecture 37 pls-37.2 (ii) Because S is a state function, there is a unique value of S (for the gas) at each point of the diagram (as is true for other state functions P , V , U , and T .) 2. Entropy and the Carnot Cycle —Carnot cycle = isotherm-adiabat cycle Fig. 2 : paths 1, 3: isotherms paths 2, 4: adiabats (i) Around the cycle A Æ B Æ C
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This note was uploaded on 03/26/2012 for the course PHY 1020 taught by Professor Kodera during the Fall '11 term at University of Florida.

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Lecture 37 - Lecture 37 pls-37.1 Entropy and the 2nd Law of...

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