Ch04-B-Gibbs energy

Ch04-B-Gibbs energy - CHM 341 Elementary Physical Chemistry...

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Chapter 4: B: Third law, Helmholtz and Gibbs energies CHM 341 Elementary Physical Chemistry Fall 2009 Ranko Richert
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1 0 ln = = = W S W k S W is number of arrangements that result in the same total energy W = 19 W = 1 at T = 0 W = 3 at T > 0 statistical entropy
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Third law of thermodynamics: The entropy of all perfect crystalline substances is zero at T = 0. 0 0 T S 1 0 ln = = = = W S W k S T dq dS rev
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residual entropy of CO residual entropy of ice (H 2 O)
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low temperatures by adiabatic demagnitization (world record low temperature is 280 pK) low spin order high entropy high spin order low entropy
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standard reaction entropy (like standard reaction enthalpy) () [] 1 1 1 1 1 1 2 2 2 2 2 2 reactants products mol J K 4 . 163 mol J K 1 . 205 2 1 30.7 1 mol J K 9 . 69 g , O 2 1 g , H l O, H C 25 at O(l) H (g) O 2 1 (g) H : of entropy reaction standard calculate ts) coefficien tric stoichiome are s ' ( Ο Ο Ο Ο Ο Ο Ο = × + = × + = ° + = m m m r m m r S S S S v vS vS S Entropy, S Ο reactants m vS Ο products m vS Ο S r S = 0 (Third law) 0
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inequality Clausius 0 T dq dS T dq T dq dS dS dS dS sur sur sur = = + spontaneous change: dG TdS dH dG G TS H G TdS dH dH TdS T dH dS dH dq dA TdS dU dA A TS U A TdS dU dU TdS T dU dS dU dq isothermal energy Gibbs 0 or or : work expansion only pressure, constant isothermal energy tz Helmhol 0 or or : work expansion only olume, constant v = = = = = = change s spontaneou for criteria 0 , 0 0 0 0 0 , , = = = = dp dT dG ,dV dT dA p T V T
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spontaneous change: isothermal, isochoric 0 0 0 , = = V T dA dV ,
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Ch04-B-Gibbs energy - CHM 341 Elementary Physical Chemistry...

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