chap19_entropy&Gibbs

E largestenergeticallyequivalentwaystoarrange itself

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Unformatted text preview: entropy • Systems process in direction that has largest energetically equivalent ways to arrange its parts • Which configuration has greater entropy; i.e., largest energetically equivalent ways to arrange itself? 6 Ludwig Boltzmann • Distribution of energy over different energy • • states used as a way to calculate entropy S = k • log W k = R/N = 1.38 x 10­23 J/K = Boltzmann constant (R = 8.314 J/mol●K & N = Avogadro’s # = 6.022 x 1023 atoms/mole) W = # of energetically equivalent ways to arrange components of system (unitless) 7 8 Standard molar entropy, S° • For standard state elements (metals, gases, etc.) molar enthalpy of formation, H°f = 0 J/mol • For entropy, it’s different: – 3rd law of thermodynamics: • The entropy of a perfect crystal at absolute zero (0K) is zero. • Since only one way to arrange (W = 1) ∀ ⇒ S = k • log W = k • log 1 = 0 9 More on entropy • Gas entropies are much larger than those for liquids • Liquid entropies are larger than solids • For ex: – I2(s) vs. Br2(l) vs. Cl2(g) standard entropies: 116.1, 152.2...
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