CH_301-Sutcliffe-Exam4

CH_301-Sutcliffe-Exam4 - Version 414 Exam 4 301 TTh...

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Unformatted text preview: Version 414 Exam 4 301 TTh sutcliffe (50985) 1 This print-out should have 26 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Which of these compounds would you expect to be a weak electrolyte? 1. Ca(OH) 2 2. All of these 3. K 2 S 4. FeS 5. CH 3 CH 2 COOH correct Explanation: 002 10.0 points Hint: The product has two central atoms, both C. Estimate the heat released when ethene (CH 2 CH 2 ) reacts with HBr to give CH 3 CH 2 Br. Bond enthalpies are C H : 412 kJ/mol; C C : 348 kJ/mol; C C : 612 kJ/mol; C Br : 276 kJ/mol; Br Br : 193 kJ/mol; H Br : 366 kJ/mol. 1. 58 kJ/mol correct 2. 424 kJ/mol 3. 470 kJ/mol 4. 1036 kJ/mol 5. 200 kJ/mol Explanation: C H H C H H + H Br C H H H C H H Br H = summationdisplay E break- summationdisplay E make = bracketleftBig (C C) + (H Br) bracketrightBig- bracketleftBig (C H) + (C Br) + (C C) bracketrightBig = (612 kJ / mol + 366 kJ / mol)- bracketleftBig 412 kJ / mol + 276 kJ / mol + 348 kJ / mol bracketrightBig =- 58 kJ / mol , so 58 kJ/mol of heat was released. 003 10.0 points Choose the formula for the compound peri- odic acid. (HIO 3 is iodic acid.) 1. HIO 3 2. HIO 2 3. H 3 IO 4. HI 5. HIO 4 correct 6. H 2 IO 2 7. HIO 8. H 2 IO 3 Explanation: 004 10.0 points When 4.00 kJ of energy is transferred as heat to nitrogen in a cylinder fitted with a piston at an external pressure of 3.00 atm, the nitro- gen gas expands from 1.00 to 4.00 L against this constant pressure. What is U for the process? 1.- 4 . 91 kJ 2. 3. +3 . 09 kJ correct 4. +4 . 91 kJ 5.- . 912 kJ Version 414 Exam 4 301 TTh sutcliffe (50985) 2 Explanation: q = 4 kJ P = 3 atm V = 1 L V f = 4 L For expansion against a constant external pressure, w =- P ext V = (- 3 atm)(4 L- 1 L) (101 . 325 J L 1 atm 1 ) =- 911 . 925 J =- . 911925 kJ . U = q + w = 4 kJ + (- . 911925 kJ) = +3 . 08807 kJ . 005 10.0 points This is a BONUS question. If you get it correct your max score is 260/250, if not, then its 250/250. Written below is a reaction in which bu- tane is formed from carbon dioxide and wa- ter. Note that this is the reverse of the butane combustion reaction. What would you say about the temperature dependence of this re- action to form butane? 8 CO 2 (g) + 10 H 2 O(g) 2 C 4 H 10 (g) + 13 O 2 (g) 1. The reaction does not occur at any tem- perature. correct 2. The reaction is more likely to occur at higher temperatures. 3. The reaction occurs at all temperatures. 4. The reaction is more likely to occur at lower temperatures. Explanation: Combustion reactions are exothermic, so the reverse of a combustion reaction is en- dothermic; i.e. , H is positive. Counting the moles of gas on each side, we have 18 mol gas 15 mol gas Therefore the overall entropy will decrease ( S is negative) and G = H- T S = (+)- T (- ) = + No matter what value of T we choose, G will always be positive, so the reaction is non- spontaneous at any temperature.spontaneous at any temperature....
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This note was uploaded on 06/07/2011 for the course CH 301 taught by Professor Fakhreddine/lyon during the Fall '07 term at University of Texas at Austin.

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CH_301-Sutcliffe-Exam4 - Version 414 Exam 4 301 TTh...

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