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# Exam04answers - Cheung Anthony Exam 4 Due Dec 6 2006 1:00...

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1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. The due time is Central time. C 6 H 5 COOH = 122.1 g/mol (benzoic acid) C 3 H 8 = 44.1 g/mol (propane) ozone is O 3 001 (part 1 oF 1) 10 points What mass oF propane (C 3 H 8 (g)) must be burned to supply 2775 kJ oF heat? The stan- dard enthalpy oF combustion oF propane at 298 K is - 2220 kJ · mol - 1 . 1. 44.1 g 2. 102 g 3. 35.3 g 4. 55.1 g correct 5. 75.9 g Explanation: 2775 / 2220 = 1.25 mol oF propane 1.25 mol × 44.1 g/mol = 55.1 g oF propane 002 (part 1 oF 1) 12 points The temperature oF 2.00 mol CO 2 (g) is in- creased From 10 C to 150 C at constant pres- sure. Calculate the change in the entropy oF carbon dioxide. Assume ideal behavior. 1. +17 . 71 J/K 2. - 11 . 70 J/K 3. +11 . 70 J/K 4. - 23 . 30 J/K 5. +23 . 30 J/K correct Explanation: T 1 = 10 C = 283 K T 2 = 150 C = 423 K n = 2 mol C p , m = 8 . 314 J mol · K Δ S = n C p , m ln µ T 2 T 1 = (2 mol) 7 2 ( 8 . 314 J mol · K ) × ln µ 423 K 283 K = 23 . 3912 J / K 003 (part 1 oF 1) 10 points Air is cooled until it Freezes and the solid air is cooled to nearly 0 K. What value does the en- tropy oF the resulting solid mixture approach as the temperature approaches 0 K? 1. A non-zero number which could be either positive or negative depending on inFormation which is not given. 2. Some positive number. correct 3. Some negative number. 4. Zero – the second law oF thermodynamics says it must. 5. Zero – the third law oF thermodynamics says it must. Explanation: The Third Law oF Thermodynamics states that the entropy oF a pure, perFect crystalline substance is 0 at absolute 0 K. Absolute en- tropy can not be negative. In this case, air is not pure, but is a mixture oF many things, and it is just a solid, not a perFect crystalline solid, so S 6 = 0. S must be some positive number in this case. 004 (part 1 oF 1) 10 points Calculate the standard enthalpy oF vaporiza- tion oF liquid bromine iF the standard en- thalpy oF sublimation oF solid bromine is +40.1 kJ · mol - 1 and the standard enthalpy oF Fusion oF solid bromine is +10 . 6 kJ · mol - 1 . 1.

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Exam04answers - Cheung Anthony Exam 4 Due Dec 6 2006 1:00...

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