PracticeChap13key

# PracticeChap13key - than decreased) temperature. 53b) You...

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Recommended Problems for Chapter 13 Oxtoby has many good problems for this chapter, so all the recommended problems are from the text. The "highly recommended" ones are close models to questions you could see on an exam, although the numerical parts would be easier to deal with. The "regular" problems are also worthwhile, but are generally either too simple, too complex, or too calculation intensive to necessarily be models for the exam. Regular Problems from Oxtoby: 1-4, 11a, 12a, 13, 14, 17-19, 21, 36-38 Highly Recommended Problems from Oxtoby: 5, 6, 9, 10, 23-32, 53, 62a Answers to all but the following odd problems are in the back of the book, and the even numbered problems are usually the same type of problem, and so should not be significantly different. 53a) S is positive. You can tell this by looking in appendix D and subtracting the difference (monoclinic has higher S than rhombic), or just by knowing that it occurs at increased (rather
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Unformatted text preview: than decreased) temperature. 53b) You could again do this just by looking in appendix D. Alternatively, you know that at 368.5 K, the process is spontaneous; for convenience, say that G = 0 rather than very slightly &gt; 0 at that temperature. If H were -400 J mol-1 , the process would always be spontaneous, so it must be +400 J mol-1 . Therefore, 0 = 400 - 368.5* S, so S = -400/-368.5 = 1.09 J mol-1 . 62a) The difference between the H vap calculated using the standard values and the actual H vap is the temperature-dependence of H. The standard values are calculated at 25 C, and the process described takes place at 76.5 C. This is an example of how H changes with temperature (actually a relatively large change; most processes will have &lt; 10% change over 100 degree ranges, rather than the 15% or so of this process). 1...
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