CH302%20Zumdahl%20Chapter%2010%20free%20energy%20review%20sp08

# CH302%20Zumdahl%20Chapter%2010%20free%20energy%20review%20sp08

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1 Chapter 10 Review Thermodynamics: Spontaneity, Entropy, and Free Energy 2 ± Spontaneous changes happen without any continuing outside influences. ± A spontaneous change has a natural direction. ± For example the rusting of iron occurs spontaneously. ± Have you ever seen rust turn into iron metal without man made interference? ± The melting of ice at room temperature occurs spontaneously. ± Will water spontaneously freeze at room temperature? Spontaneous Changes 3 Spontaneous Changes ± A spontaneous change in a process has a natural tendency to occur. ± The change does not necessarily occur rapidly ± A nonspontaneous change in a process can be brought about only by doing work.

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4 ± The common characteristic that causes processes to spontaneous in only one direction comes from many years of observations. ± The increase in a property called entropy appears to responsible for spontaneity in processes. ± The change in the entropy of the universe for a given process is a measure of the driving force behind that process. Entropy and Disorder 5 ± Energy and matter tend to become more disordered. ± In thermodynamics, this idea of a tendency toward disorder is call entropy (S). ± High disorder represents high entropy . ± Low disorder represents low entropy. Entropy and Disorder 6 The Second Law of Thermodynamics The second law of thermodynamics states, “ In spontaneous changes the universe tends towards a state of greater disorder .” ± Spontaneous processes have two requirements: 1. The entropy (disorder) of the universe must increase. ± Fundamentally, the system must be capable of doing useful work on surroundings for a spontaneous process to occur. 2. The free energy change of the system must be negative.
7 ± Entropy is a measure of the disorder or randomness of a system. ± As with H, entropies have been measured and tabulated in Appendix four as S o 298 ± When: ± S > 0 disorder increases (which favors spontaneity). ± S < 0 disorder decreases (does not favor spontaneity). Changes in Entropy 8 ± The disorder of a system is expected to increase when heat is added because the additional heat energy increases the thermal motion of the molecules. ± Heating increases the thermal disorder . ± Increasing thermal disorder increases the ranges of different energies that the molecules can have. Changes in Entropy 9 ± The disorder of a system is expected to increase when a given amount of matter spreads into a greater volume or is mixed with another substance. ± Spreading the molecules of a substance into additional locations increases the positional disorder . ± The larger volume provides more locations for the molecules and increases positional disorder. ± An increase in positional disorder increases the entropy of the system.

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## This note was uploaded on 09/20/2008 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas at Austin.

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CH302%20Zumdahl%20Chapter%2010%20free%20energy%20review%20sp08

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