Exam_4 - Version 401 Exam 4 McCord (53110) 1 This print-out...

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Unformatted text preview: Version 401 Exam 4 McCord (53110) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. McCord CH301mwf This exam is only for McCords MWF CH301 class. PLEASE carefully bubble in your UTEID and Version Number! Youll need some (not all) of the values from this table on the exam. H f G f S Substance ( kJ mol ) ( kJ mol ) ( J mol K ) CO(g)- 110 . 53- 137 . 17 197.67 CO 2 (g)- 393 . 51- 394 . 36 213.74 SO 2 (g)- 296 . 83- 300 . 19 248.22 H 2 O(l)- 285 . 83- 237 . 13 69.91 H 2 O(g)- 241 . 82- 228 . 57 188.83 H 2 S(g)- 20 . 63- 33 . 56 205.79 CH 3 OH(l)- 238 . 86- 166 . 27 126.8 CH 4 (g)- 74 . 81- 50 . 72 186.26 C 2 H 4 (g) +52 . 26 +68 . 12 219.56 C 3 H 8 (g)- 103 . 85- 23 . 49 270.2 C 4 H 10 (g)- 126 . 15- 17 . 03 310.1 C 6 H 6 ( ) +49 . +124 . 5 173.3 C 8 H 18 ( )- 249 . 9 +6 . 4 358 001 10.0 points Calculate the change in entropy when 2.00 moles of ozone are compressed isothermally to one quarter of its original volume. Treat ozone as an ideal gas. 1.- 1.39 J K 1 2. +23.1 J K 1 3.- 23.1 J K 1 correct 4. +10.0 J K 1 5.- 10.0 J K 1 Explanation: If compressed to one quarter the original volume this means V 2 = V 1 4 or V 2 V 1 = 1 4 S = nR ln parenleftbigg V 2 V 1 parenrightbigg = (2 . 00 mol)(8 . 314 J mol 1 K 1 ) ln parenleftbigg 1 4 parenrightbigg =- 23 . 0513 J K 1 We expect a negative answer since the volume decreased. 002 10.0 points Calculate the standard reaction enthalpy for the reaction N 2 H 4 ( ) + H 2 (g) 2 NH 3 (g) given N 2 H 4 ( ) + O 2 (g) N 2 (g) + 2H 2 O(g) H =- 543 kJ mol 1 2 H 2 (g) + O 2 (g) 2 H 2 O(g) H =- 484 kJ mol 1 N 2 (g) + 3 H 2 (g) 2 NH 3 (g) H =- 92 . 2 kJ mol 1 1.- 243 kJ mol 1 2.- 151 kJ mol 1 correct 3.- 59 kJ mol 1 4.- 1119 kJ mol 1 5.- 935 kJ mol 1 Explanation: We need to reverse the second reaction and add them: Version 401 Exam 4 McCord (53110) 2 N 2 H 4 ( ) + O 2 (g) N 2 (g) + 2 H 2 O(g) H =- 543 kJ/mol 2 H 2 O(g) 2 H 2 (g) + O 2 (g) H = +484 kJ/mol N 2 (g) + 3 H 2 (g) 2 NH 3 (g) H =- 92 . 2 kJ/mol N 2 H 4 ( ) + 3 H 2 (g) 2 H 2 (g) + 2 NH 3 (g) N 2 H 4 ( ) + H 2 (g) 2 NH 3 (g) H =- 151 . 2 kJ/mol 003 10.0 points Which one of the following reactions has a positive entropy change? 1. BF 3 (g) + NH 3 (g) F 3 BNH 3 (s) 2. N 2 (g) + 3 H 2 (g) 2 NH 3 (g) 3. 2 NH 4 NO 3 (s) 2 N 2 (g) + 4 H 2 O(g) + O 2 (g) correct 4. H 2 O(g) H 2 O( ) 5. 2 SO 2 (g) + O 2 (g) 2 SO 3 (g) Explanation: Processes that result in an increase in the number of moles of gaseous substances have S sys > 0. Only this choice demonstrates an increase in the number of moles of gaseous substances (from 0 moles of gaseous reactants to 7 moles of gaseous products)....
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This note was uploaded on 04/30/2011 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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Exam_4 - Version 401 Exam 4 McCord (53110) 1 This print-out...

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