Unformatted text preview: ENTROPY — "a measure of disorder" 1. S = kan is the deﬁning equation from statistical mechanics. 2. Q is the number of microstates available for a system. When there is only one way to
arrange the particles of the system, Q=l and S=0 (i.e., absolute zero point for entropy; e.g.,
homogeneous material at absolute zero temperature or all white marbles on a Chinese
checkerboard). 3. During ﬁrst order phase changes (i.e., melting and boiling) the order of the molecules is
clearly changing and we can easily ﬁgure out the direction (e.g., crystal to liquid = QT and is
discontinuous), hence the direction of entropy change for the system is easy to imagine based on
the Boltzman equation for entropy. 4. Sensible heating of a system excites the molecules more (i.e., the amount of Vibration,
translation, and rotation increases) so QT and ST. 5. Cooling through phase changes or sensible cooling causes the opposite effect. 6. The statistical way of looking at entropy is broadly applicable to microscopic and
macroscopic thermodynamics. 7. For energy, it is difficult to deﬁne any absolute zero of energy. Even at absolute zero
temperature, the atoms still have a strong and weak nuclear force as well as the electrostatic
potential holding the stuff together. 8. The direction of spontaneous processes must always occur in the direction of globally
increasing entropy, but the entropy change of a system can go up or down (e.g., melting or
freezing). 3.}. 5...? alts/anus ...
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 Spring '08
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 Chemical Engineering

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