quiz_answers_Quiz_02_key_152A

Quiz_answers_Quiz_02 - 2(4pt For each of the following statements indicate whether it is true or false a T or F A spontaneous reaction always

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Chem 152 A Winter 2008 Name________________ Quiz #2 Section______________ Score_______out of 10pt Answer Key 1. (3pt) The heat of combustion of acetylene, C 2 H 2(g) at 25 ° C is roughly -1300 kJ/mol. At this temperature, H ° f value for CO 2 , and H 2 0 are roughly -400 kJ/mol and -300 kJ/mol, respectively. a) Write the balanced chemical equation for the combustion of acetylene 2 C 2 H 2(g) + 5 O 2(g) Æ 4 CO 2(g) + 2 H 2 O (l) b) Calculate H ° f H ° rxn = H ° f (Products) - H ° f (Reactants) = [(4 x -400 kJ/mol) + (2 x -300 kJ/mol)] – (2x H ° f (C 2 H 2(g) )) = 2x(-1300) kJ/mol H ° f (C 2 H 2(g) ) = +200 kJ/mol If you used -1300 kJ/mol as the H ° f of C 2 H 2(g) H ° rxn = H ° f (Products) - H ° f (Reactants) = [(4 x -400 kJ/mol) + (2 x -300 kJ/mol)] – (2 x -1300 kJ/mol) = 400 kJ/mol
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Unformatted text preview: 2. (4pt) For each of the following statements, indicate whether it is true or false a) T or F A spontaneous reaction always releases heat b) T or F The entropy of a system always increases for a spontaneous change c) T or F The entropy of a system and its surroundings always increases for a spontaneous change d) T or F The energy of a system always increases for a spontaneous change 3. (3pt) When liquid CCl 4 evaporates, it absorbs 30.0 kJ/mol of heat at 27 ° C. Calculate the change in entropy, ∆ S. ∆ S sys = (30.0 kJ/mol )/ 300 K = +100 J/mol K or ∆ S surr = -(30.0 kJ/mol )/ 300 K = -100 J/mol K...
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This note was uploaded on 04/12/2008 for the course CHEM 152 taught by Professor Chiu during the Winter '08 term at University of Washington.

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