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11.09.2011 - Chem 260 November 9 2011#$ 93%<#$'0 1...

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Chem 260 November 9, 2011 Lecture 27 1 !"#$%&'() +,- .#/'0(# +1 234#$5#( 67 +-88 93:;) %< !"#$%&'() +,- " #$%& $' ()**+ &'&%,- " ()**+ &'&%,-. /0/)1/*1& &'&%,-. /'2 3$%4 .;'#( %< !"#$%&'() +,- " %&/2)',5 678 9 :;<=> ? 678 @ :;<=> " A7/+& BCD)1)*%)/ " #)EFD%&+ "#)2F&%G H$0&G*&% IJ8 K5LLM8 N$$G IKLL8 ":+D*G)F / '$F& O 2&F/)1)', / P$'Q1)PFR&EF&'2&2 F)G& '&&2+> The Three Laws of Thermodynamics 1. 2. 3. ! U = q + w Energy Conservation ! S " 0 everything tends toward increasing disorder S > 0 except for perfect crystals at T = 0 K The internal energy of an isolated system is constant The entropy of the universe tends to increase The entropy of a perfectly crystalline substance is zero at T = 0 K You can ` t win, the best you can do is break even You can only break even at absolute zero You can never reach absolute zero Atkins Moore Summary: The energy of the universe is constant; the entropy of the universe tends always toward a maximum. Rudolf Julius Clausius (1822-1888) ! H r > 0 ! H r < 0 ! H r > 0 ! H r < 0 ! S r < 0 ! S r > 0 ! S r > 0 ! S r < 0 Enthalpy Entropy Exothermic? Spontaneous? endothermic endothermic exothermic exothermic l heat required z l heat required z l heat released z l heat released z NO YES entropy driven enthalpy driven When will a chemical reaction occur spontaneously? Energy must be conserved First Law but . .. Entropy Rules! Second Law ! S UNIV < 0 ! S UNIV > 0 ! S r > ! H r T IF !" H r T > !" S r IF The 2 nd Law in terms of a chemical system ! S uni = ! S sys + ! S surr " 0 system state function
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11.09.2011 - Chem 260 November 9 2011#$ 93%<#$'0 1...

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