ch18 MSJ jlm - Chapter 18 Chapter Thermodynamics:...

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Chapter 18 Chapter 18 Thermodynamics: Directionality of Chemical Reactions Ludwig Boltzmann 1844-1906. Famous for his equation statistically defining entropy. Josian W. Gibbs 1839-1903. Pioneered concepts of chemical thermodynamics and free energy.
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So far, we have tried to answer the following questions: (1) What are the energetics (heat) of a reaction? Is it exothermic ( H= -) or endothermic ( H= +)? (2) How fast (kinetics) and how (mechanism) does the reaction go? (3) To what extent does it go? (equilibrium) (4) Does it go, i.e., is it spontaneous? This is the subject of this chapter. And finally now ……. .
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Spontaneous processes: defined descriptively as a process that occurs by itself (and the reverse does not occur by itself) hot cold The opposite: hot cold is not spontaneous, but, it is possible (how does a refrigerator work?). Other spontaneous processes (ask yourself: does reverse ever occur by itself ?) nail rusting eggs breaking (Humpty Dumpty) paper burning water freezing at -10 o C ice melting at +10 o C gases mix heat heat is spontaneous,
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All of these spontaneous processes are also described as: irreversible There are reversible processes, but the systems must be at equilibrium . heat + ice → water at +10 o C Spontaneous, irreversible heat + ice ← water at -10 o C Spontaneous, irreversible heat + ice water at 0 o C Reversible; equilibrium Both ice and water coexist at 0 o C Either process, → or ← can occur at equilibrium Irreversibility Spontaneity
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(irreversible)? Exothermic reactions tend to be spontaneous (exception, dissolving ammonium salts), and increasing entropy (randomness) tends to cause processes to be spontaneous; but overall Gibbs Free Energy must decrease in order for a process to be spontaneous. A
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This note was uploaded on 04/12/2011 for the course CHEM 1420 taught by Professor Acree during the Spring '08 term at North Texas.

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ch18 MSJ jlm - Chapter 18 Chapter Thermodynamics:...

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