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Unformatted text preview: Version 010 Exam Four: Shear Shear (52375) 1 This print-out should have 25 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 300, and it counts equally with all previous inclass exams. 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 dont 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 scantron sheet 001 10.0 points Which statement would be the best interpre- tation of the First Law of Thermodynamics? 1. The total amount of energy in the uni- verse is constant. correct 2. The total amount of entropy in the uni- verse is increasing. 3. The total amount of energy in the uni- verse is increasing. 4. The total amount of matter in the uni- verse is constant. Explanation: The first law is the law of conservation of energy and mass (not matter). The second law deals with entropy. 002 10.0 points For a reaction in which more moles of gas are produced than are consumed, E is 1. the same as H . 2. unrelated to H . 3. more positive than H . 4. less positive than H . correct Explanation: From the equation H = E + ( n ) RT if n is positive (more moles of gas produced), then H must be larger than E ; in other words, E is less positive than H . Alternate Solution: E = q + w q = H w =- P V =- ( n ) RT For this situation, n &gt; 0, so w &lt; 0. E = q + E = H + w , so E &lt; H . 003 10.0 points The best definition of heat is 1. potential energy. 2. temperature. 3. the transfer of energy. correct 4. vibrational energy. 5. kinetic energy. Explanation: Heat flows spontaneously from a hotter body to a colder body. 004 15.0 points For the reaction 2 SO 3 (g) 2 SO 2 (g) + O 2 (g) H r = +198 kJ mol 1 and S r = 190 J K 1 mol 1 at 298 K. The forward reaction will be spontaneous at 1. all temperatures. Version 010 Exam Four: Shear Shear (52375) 2 2. no temperature. 3. temperatures below 1042 K. 4. temperatures above 1042 K. correct 5. temperatures above 1315 K. Explanation: H r = +198 kJ / mol S r = 0 . 019 kJ mol K G = H- T S G &lt; 0 for a spontaneous reaction, so &gt; H- T S T &gt; H S = 198 kJ / mol . 019 kJ mol K = 1042 . 11 K Thus the temperature would need to be &gt; 1042 . 11 K. 005 10.0 points When a gas expands into a vacuum, w = 0. 1. True correct 2. False Explanation: No work is done when a gas expands into a vacuum since there is nothing to push out of the way....
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- Spring '09