Lecture_39_PPT

Lecture_39_PPT - Chapter 22 Entropy and the Second Law of...

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Chapter 22 Entropy and the Second Law of Thermodynamics
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Second Law of Thermodynamics z For an isolated system, its entropy can never decrease with time. z Establishes which processes do and which do not occur z Some processes can occur in either direction according to the first law z Some are observed to occur only in one direction - Irreversible Processes z This directionality is governed by the second law
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Entropy Order Disorder z Entropy is a natural measure of disorder, a measure of randomness. z The more disorder a system is, the high entropy it has. z Entropy is a state variable related to the second law of thermodynamics
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Entropy is a State Variable P, V, T, E, N P, V, T, E, N S=3( N/3 k B ln (V/ v )) = N k B ln (V/ v ) N/3 N/3 N/3 S= Nk B ln (3V/ v )
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Entropy and Heat z Q = T S >0 T i , N i , E i , S i T f , N f , E f , S f z Let dQ r be the amount of energy transferred by heat when a system follows a reversible path z The change in entropy is r dQ dS T = z W < 0 z E int = Q + W = 0
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Energy, Entropy and Work z The change in entropy, r dQ dS T = dE int = dQ + dW = TdS + dW E int = Q + W T E S E- d E S- d S dW dQ=TdS z In any process where the system gives up energy dE and its entropy falls by dS , a quantity at least TdS of that energy must be given up to the system's surroundings as unusable heat.
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This note was uploaded on 01/28/2011 for the course PHYS 011 taught by Professor Nianlin during the Fall '08 term at HKUST.

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Lecture_39_PPT - Chapter 22 Entropy and the Second Law of...

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