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# che4 - Version 244 Exam 4 Shear shear(52375 This print-out...

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Version 244 – Exam 4: Shear – shear – (52375) 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. DrRuth says: In all cases, select the answer that BEST answers the question asked. The total points on this exam is 375, but it counts equally with the previous exams that were worth 400 points. Read the whole thing first and plan which to answer first because you feel confident about them. Notice the harder ones and save them up till last so you don’t use up all your time working on them. Shear 52375 1 L atm = 101.325 J 1 cal = 4.184 J R = see back of answer sheet 001 10.0 points Hot coffee in a vacuum flask (thermos) is an example of what type of system? 1. open 2. closed 3. isolated correct Explanation: An isolated system cannot exchange energy nor matter with the surroundings. 002 10.0 points Consider the following substances: HCl(g) F 2 (g) HCl(aq) Na(s) Which response includes ALL of the sub- stances listed where Δ H 0 f is NOT equal to zero? 1. Na(s) and F 2 (g) 2. Na(s) 3. HCl(g), Na(s) and F 2 (g) 4. HCl(g) and HCl(aq) correct 5. HCl(g), Na(s), HCl(aq) and F 2 (g) Explanation: Δ H 0 f = 0 for elements in their standard states. This would be true for both Na(s) and F 2 (g). 003 20.0 points The molecules in the reaction NH 3 (g) + 3 F 2 (g) NF 3 (g) + 3 HF(g) contain only single bonds. What is the heat evolved or absorbed per mole of NH 3 that reacts? These bond energy values might be useful: H-F 566 kJ/mol, F-F 158 kJ/mol, N-H 391 kJ/mol, N-F 272 kJ/mol. 1. -289 kJ/mol 2. +867 kJ/mol 3. - 867 kJ/mol correct 4. None of these 5. +1105 kJ/mol 6. - 1105 kJ/mol 7. +151 kJ/mol 8. - 566 kJ/mol Explanation: 3(391)+3(158)-3(272)-3(566) = -867 004 25.0 points Calculate the reaction enthalpy for the com- bustion of ethanol CH 3 CH 2 OH + 3 O 2 2 CO 2 + 3 H 2 O given the data C 2 H 2 + 5 2 O 2 2 CO 2 + H 2 O Δ H rxn = - 1300 kJ/mol C 2 H 2 + H 2 C 2 H 4 Δ H rxn = - 175 kJ/mol

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Version 244 – Exam 4: Shear – shear – (52375) 2 C 2 H 4 + H 2 O CH 3 CH 2 OH Δ H rxn = - 44 kJ/mol H 2 + 1 2 O 2 H 2 O Δ H rxn = - 286 kJ/mol 1. - 1800 kJ/mol 2. None of these is correct. 3. - 1761 kJ/mol 4. - 1367 kJ/mol correct 5. - 1717 kJ/mol Explanation: 005 10.0 points The best definition of heat is 1. temperature. 2. vibrational energy. 3. kinetic energy. 4. potential energy. 5. the transfer of energy. correct Explanation: Heat flows spontaneously from a hotter body to a colder body. 006 10.0 points For a given reaction Δ G is very negative. Which of the following is FALSE? 1. If Δ S is positive, then the reaction will probably be more spontaneous at higher tem- peratures. 2. Δ S for the reaction may be positive or negative. 3. The reaction should occur very rapidly because Δ G is very negative. correct 4. The entropy of the universe must increase as a result of this reaction occuring. 5. The reaction is termed spontaneous.
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