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Chem 162-2011 lecture 17 truncated

# Chem 162-2011 lecture 17 truncated - CHEMISTRY 162-2011...

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CHEMISTRY 162-2011 Lecture 17 Ed Tavss, PhD ANNOUNCEMENTS E-MAIL ATTENDANCE Sign in EXAMS Based on an analysis last year at this time, I have no students who attend class who are mathematically eliminated from a B, and many who are not eliminated from an A. Don’t give up if you’ve done poorly. How did we do? QUIZ M,W: 16.4-16.6 W: 16.5-20.8 Th,F: 20.7-17.3 MISCELLANEOUS Chem 162-2011 Lecture 17 1

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PLAN FOR TODAY CHAPTER 17 - SPONTANEITY, ENTROPY AND FREE ENERGY 17.1 Why study thermodynamics? 17.2 Spontaneous change 17.3 The concept of entropy 17.4 Free energy and free energy change Chem 162-2011 Lecture 17 2
CHAPTER 16 - SPONTANEITY, ENTROPY AND FREE ENERGY First law of thermodynamics: Energy can neither be created nor destroyed. Second law of thermodynamics: The entropy of the universe always increases in a spontaneous process. Third law of thermodynamics: The entropy of a perfectly ordered crystalline substance at 0 K is zero. Entropy describes the number of arrangements (positions and/or energy levels) available to a system. Entropy is (officially called chaos, disorder, randomness) positional freedom, or positional availability, or disorder, or being unconfined positionally or escape from positional confinement or freedom from positional confinement ΔG o = Σn p ΔG o f(products) - Σn r ΔG o f(reactants) ΔH o = Σn p ΔH o f(products) - Σn r ΔH o f(reactants) ΔS o system = Σn p S o products - Σn r S o reactants ΔS system = Σn p S products - Σn r S reactants (used for ΔS system anytime ) ΔS system = ΔH system /T (used for ΔS system only when at equilibrium) ΔS surr = ΔH surr /T = -ΔH system /T (used for ΔS surr anytime) ΔS univ = ΔS sys + ΔS surr Four ways to find ΔG o : (1) ΔG o = ΔH o - TΔS o (or ΔG = ΔH - TΔS) At equilibrium ΔG = 0 0 = (ΔH - TΔS) ΔS system = ΔH system /T Trouton’s rule: At normal B.P., ΔS vaprization ≈ 87J mol -1 K -1 (2) ΔG o = Σn p ΔG o f(products) - Σn r ΔG o f(reactants) (3) ΔG T o = ΔG 1 o + ΔG 2 o (i.e., adding equations [Hess’s law]) (4) ΔG o = -RT ln(K) ΔG = ΔG o + RT ln(Q) (Q can be any pressure or concentration) w max = ΔG ln(K 2 /K 1 ) = (∆H o /R)((1/T 1 ) – (1/T 2 )) Chem 162-2011 Lecture 17 3

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TERMINOLO GY System: That part of the universe we are studying (e.g., Fe filings + oxygen) Surroundings: The rest of the universe (e.g., the steel bomb, the H 2 O, you, me) Chem 162-2011 Lecture 17 System Surroundings (sample + O 2 ) 4
TERMINOLOGY (CONT.) In Thermodynamics we will be dealing with three parameters, - ∆H (change in enthalpy [heat]) - ∆S (change in entropy [positional freedom] - ∆G (change in Gibbs Free Energy [sum of the ∆S and ∆H terms]). Chem 162-2011 Lecture 17 5

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TERMINOLOGY (CONT.) SPONTANEOUS PROCESS Sociology spontaneity definition: An impulsive action coming from a sudden inclination; e.g., a spontaneous outburst of applause. Spontaneity not related to speed Chemistry spontaneous definition: the ability of a reaction to take place unassisted Will the reaction go to the right?
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Chem 162-2011 lecture 17 truncated - CHEMISTRY 162-2011...

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