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• 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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This note was uploaded on 01/17/2014 for the course PHY 53890 taught by Professor Appling during the Fall '13 term at University of Texas.
- Fall '13