Lec08_drobny_11 - Lecture 8: The Second and Third Laws of...

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Lecture 8: The Second and Third Laws of Thermodynamics • Reading: Zumdahl 10.5, 10.6 • Recommended Problems:10.31, 10.35, 10.37, 10.41, 10.45 • Outline – DeFnition of the Second Law – Determining ! S – DeFnition of the Third Law
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The Second Law • The Second Law: In any spontaneous process , there is always an increase in the entropy of the universe . • From our de±nitions of system and surroundings: ! S universe = ! S system + ! S surroundings
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The Second Law (cont.) • Three possibilities: – If ! S univ > 0…. .process is spontaneous – If ! S univ < 0…. .process is spontaneous in opposite direction. – If ! S univ = 0….equilibrium Here’s the catch: We need to know ! S for both the system and surroundings to predict if a reaction will be spontaneous!
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The Second Law (cont.) • Consider a reaction driven by heat fow From the surroundings at constant P. – Exothermic Process: ! S surr = heat/T – Endothermic Process: ! S surr = -heat/T • Heat transFerred = q P,surr = - q P,system= - ! H sys
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Calculating Entropy ! T = 0 ! V = 0 ! P = 0
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Example: What is ! S for the heating of a mole of a monatomic gas isochorically from 298 K to 350 K? 3/2R
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Lec08_drobny_11 - Lecture 8: The Second and Third Laws of...

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