homework_452hmwk6 - Chem 452 Homework Set #6 (Full Set)...

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©2010 Sarah L. Keller Chem 452 Homework Set #6 (Full Set) General Hints. Several questions are qualitative. To make your lives easier, just write shor t answers! Also, if you are starting this set early, you might begin with problems 2, 3, 4, and 8. --------------------------------------------------------------------------------------------------------------- 1) We hope to return Midterm #1 in class/office hours starting Monday, Feb 8. On the same date, the answers will be posted in the Chem452 bulletin board in the hallway right outside our classroom (BAG 154). I will not post answers online. I’ve found that students understand the answers better if they write the answers by hand. (Why is that true? Beats me!) a) Now that you have the luxury to slowly read all the problems, which problem(s) do you find most intellectually interesting? (there is no right answer on this one.) b) Choose one of the long problems that you made mistakes on or didn’t have time to do. Try it again and check your answers. Write the full question and correct answer. Make sure you understand it, and what you might have missed or not had time to do the first time. 2) Describe in one short phrase whether ± S will generally increase or decrease in the following: a) Neutralization of charges in an aqueous solution b) A polar molecule is placed in a nonpolar solvent (or the opposite) c) DNA is mixed with cationic lipids in an aqueous solution, which is a current proposed method to deliver DNA into cells for gene therapy. Drawing a picture may be helpful. d) A phase change from a gas to a liquid e) Increasing the number of molecules in the system (i.e. doubling the system) f) Increasing the temperature of the system g) Stretching a rubberband 3) The second law of thermodynamics states that entropy increases for spontaneous processes and that an increase in entropy is associated with transitions from ordered to disordered states. Living organisms, even the simplest bacteria growing in cultures, appear to violate the second law because they grow and proliferate spontaneously. They convert simple chemical substances into the highly organized structure of their descendants. Evaluate the proposition that living organisms contradict the second law. Be sure to state your conclusions clearly. (You do not need to write an essay – just a couple of sentences is fine.) (Taken from Tinoco’s text, Problem 3.3) 4) Consider a process where n A mol of gas A initially at 1 atm pressure mix with n B mol of gas B also at 1 atm to form 1 mol of a uniform mixture of A and B at a final total pressure of 1 atm, and all at constant temperature T. Assume that all gases behave ideally. (Parts a and b taken from Tinoco’s text, problem 3.4) a) Show that the entropy change, ± S mix , for this process is ± S mix = ² X A RlnX A ² X B RlnX B , where X A and X B are the mole fractions of A and B, respectively. Hint: We did this in class. Set initial volumes = V A and V B , and final volume = V. b) What can you say about the value (especially the sign) of
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homework_452hmwk6 - Chem 452 Homework Set #6 (Full Set)...

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