chem exam3laude - Warsi, Kusum Exam 3 Due: Dec 7 2006, 4:00...

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Warsi, Kusum – Exam 3 – Due: Dec 7 2006, 4:00 pm – Inst: David Laude 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. The due time is Central time. Please remember to write down your ver- sion number. GOOD LUCK! 001 (part 1 oF 1) 6 points The combustion oF a certain amount oF methane produces 100 kJ oF energy. Dur- ing this process the amount oF energy in the universe 1. decreases by 100 kJ. 2. does not increase nor decrease. correct 3. The answer cannot be determined with- out knowing the chemical equation For this reaction. 4. increases by 100 kJ. Explanation: According to the ±irst Law oF Thermody- namics, the total amount oF energy in the universe is constant. 002 (part 1 oF 1) 6 points Calculate Δ S surr at 298 K For the reaction 6C(s) + 3H 2 (g) C 6 H 6 ( ) Δ H r = +49.0 kJ · mol - 1 and Δ S r = - 253 J · K - 1 · mol - 1 . 1. - 253 J · K - 1 · mol - 1 2. +164 J · K - 1 · mol - 1 3. +253 J · K - 1 · mol - 1 4. - 417 J · K - 1 · mol - 1 5. - 164 J · K - 1 · mol - 1 correct Explanation: 003 (part 1 oF 1) 6 points A 50 gram sample oF delicious pork rinds is placed in an open, constant pressure calorime- ter that contains 3000 grams oF water. The temperature oF the water increases by 47 C when the pork rinds are combusted. The heat capacity oF water is 4.184 J/g C. Assume the heat lost to the calorimeter itselF or to the air is negligible. Which oF the Following is correct For the SYSTEM? 1. Δ H = +590 kJ 2. Δ U = - 11 . 8 kJ 3. Δ U = +11 . 8 kJ 4. Δ H = - 11 . 8 kJ 5. Δ H = - 590 kJ correct 6. Δ U = +590 kJ 7. Δ H = +11 . 8 kJ 8. Δ U = - 590 kJ Explanation: At constant pressure q p = Δ H . q cal = m H 2 O c p Δ T = (3000 g)(4 . 184 J / g C)(47 C) = 589944 J = 589 . 944 kJ Thus q sys = - q cal = - 589 . 944 kJ. 004 (part 1 oF 1) 6 points ±or a certain reaction Δ H is 0.00159114 kJ and Δ S is 1.1 J/K. This reaction can become spontaneous only above some temperature. What is this temperature? 1. 1.445 C 2. - 0.00445 C 3. 0.00145 C 4. - 271.55 C correct
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Warsi, Kusum – Exam 3 – Due: Dec 7 2006, 4:00 pm – Inst: David Laude 2 5. - 418.82 C 6. 691.82 C 7. 271.55 C 8. 418.82 C 9. - 691.82 C 10. - 1.445 C Explanation: 005 (part 1 of 1) 6 points Consider the reaction CH 4 (g) + I 2 (g) CH 3 I(g) + HI(g) Bond energy tables give the following values: C H : 416 kJ/mol I I : 151 kJ/mol H I : 299 kJ/mol C I : 213 kJ/mol This reaction is 1. endothermic by about 55 kJ/mol. cor- rect 2. endothermic, but insuFcient information given to say by how much. 3. endothermic by about 206 kJ/mol. 4.
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This note was uploaded on 02/25/2010 for the course CH 54363 taught by Professor Mccord during the Spring '08 term at University of Texas.

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chem exam3laude - Warsi, Kusum Exam 3 Due: Dec 7 2006, 4:00...

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