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# 2300_les16 - VI Entropy A Introduction 1 The first law energy cannot be created or destroyed 2 The second law certain processes do occur and

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1 lesson 16 VI. Entropy A. Introduction 1. The first law: energy cannot be created or destroyed 2. The second law: certain processes do occur and certain processes don’t 3. The magic vortex tube. Will it work or won’t it ? Magic Vortex Tube Compressed air 2 kg at 4 atm, 300 K Hot air 1 kg at 1 atm, 333 K Cold air 1 kg at 1 atm 273 K We need a quantitative answer. This suggests that we are looking for a property (like T, P, u, or V). How can we find such a property? lesson 16 VI. Entropy B. The Clausius Inequality Rev. Heat Engine T H T L Q L Q H W out,net For a reversible heat engine, (6-16), is HL rev QQ Q or 0 TT T δ = = v For an irreversible heat engine, with Q H constant, irrev L,irrev L,rev Q Q Q or or 0 T >< < v In general, we have the Clausius inequality, Q 0 T v (7-1) H L H L T T Q Q = and

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2 lesson 16 VI. Entropy C. A New Property Called Entropy The equality in (7-1) holds for a reversible process, the inequality for an irreversible one. Q 0 T δ v (7-1) We know that the cyclic integral of a property is zero. Clausius recognized that the equality in (7-1) implies the existence of a new property, entropy, which we will give the symbol S. rev Q 0o r dS 0 T == ∫∫ vv (7-4) = K kJ T Q dS rev and Equation 7-4 can also be written as rev Q dS kJ dt T s K ⎛⎞ = ⎜⎟ ⎝⎠ ± lesson 16 VI. Entropy Equation 7-4 can be used to calculate changes in entropy for an internally reversible, isothermal heat transfer process. As previously noted, isothermal heat transfer processes are internally reversible
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## This note was uploaded on 09/04/2009 for the course CHEM 2300 taught by Professor Thermo during the Summer '08 term at University of Utah.

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2300_les16 - VI Entropy A Introduction 1 The first law energy cannot be created or destroyed 2 The second law certain processes do occur and

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