Thermo_2.docx - A system can only gain order at the expense...

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- 1 - BIOL 7110 / 4105 / CHEM 8901 / 4804 THERMODYNAMICS – II. 4. Second Law of Thermodynamics: The Universe Tends Toward Maximum Disorder Entropy: A state function describing disorder The laws of probability cause any system of reasonable size to spontaneously adopt its most probable arrangement. This arrangement is the one at which entropy is a maximum. The system adopts this state simply because it is so overwhelmingly probable. Example: N molecules contained in two flasks. For any constant energy process ( Δ E = 0), a spontaneous process requires Δ S > 0. At equilibrium, no spontaneous change in the system is possible, so S is a maximum. Since the energy of the universe is constant, any spontaneous process must cause the entropy of the universe to increase. For any spontaneous process Δ S system + Δ S surroundings = Δ S universe > 0 The second law of thermodynamics is thus a consequence of the first law, plus simple probability theory. The second law does not forbid the ordering of a particular system.
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Unformatted text preview: A system can only gain order at the expense of disordering its surroundings to an even greater extent. It is sometimes stated that "life feeds on negative entropy (negentropy)." Measurement of entropy for a reversible process at constant temperature: S = Q/T Equation [5] For any real spontaneous process, the entropy change of the universe is always greater than the ideal (reversible) value. S > Q/T When a system departs from an initial state and then returns to the initial state by any real process, the entropy of the universe must increase, even though the entropy of the system (a state function) does not change. Cannot generally use the second law as a criterion to determine if a process will occur. Can sometimes measure S system , but almost never can measure S universe . Need some other state function to determine which processes will occur spontaneously....
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