Homework 1-solutions - alexander (jra2623) Homework 1...

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Unformatted text preview: alexander (jra2623) Homework 1 sutcliffe (51045) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points If G rxn is positive, then the forward reaction is (spontaneous / nonspontaneous) and K is (less / greater) than one. 1. nonspontaneous; greater 2. spontaneous, greater 3. None of these; G is not directly related to K . 4. spontaneous, less 5. nonspontaneous; less correct Explanation: A positive G rxn (standard reaction free energy) denotes an endothermic reation, which is nonspontaneous. Also, G rxn =- RT ln K , so a positive G rxn would result in a K that is between the values of zero and one. 002 10.0 points Which combination of G and K is im- possible? 1. G = 60 . 9 J, K = 4 . 67 10 10 correct 2. G =- 98 . 7 J, K = 1 . 04 3. G =- 55 . 1 kJ, K = 4 . 5 10 9 4. G = 64 . 9 kJ, K = 4 . 27 10 12 5. G = 99 . 6 J, K = 0 . 961 Explanation: If G is positive, K must be less than 1; if G is negative, K must be greater than 1. Also, if G is small (compared to RT), then K will be close to 1, and if G is large, K will be much smaller or greater than 1. 003 10.0 points When G is calculated for a proposed reac- tion, the process being described is 1. any mixture of reactants and products converted to equilibrium mixture. 2. any mixture of reactants converted to equilibrium mixture. 3. 100% reactants converted to 100% prod- ucts. correct 4. 100% reactants converted to equilibrium mixture. Explanation: G = G final- G initial = G products- G reactants 004 10.0 points Note: The reaction progress axis reads from all reactants (far L) to all products (far R) The figure represents a reaction at 298 K. b b b b b G A B C D E rxn progress Based on the figure, the standard reaction is 1. spontaneous. correct 2. nonspontaneous. Explanation: G is negative (point E is lower free en- ergy than point A), so the standard reaction is spontaneous. 005 10.0 points A gas-phase reaction has K p = 6 . 34 10 20 at 25 C. Calculate G for this reaction. Correct answer:- 118 . 697 kJ / mol rxn. Explanation: alexander (jra2623) Homework 1 sutcliffe (51045) 2 K p = 6 . 34 10 20 T = 25 C + 273 = 298 K G =- RT ln K p =- (8 . 314 J / mol K) (298 K) ln ( 6 . 34 10 20 ) =- 118 . 697 kJ / mol rxn 006 10.0 points Consider the reaction 2 Fe 2 O 3 (s) + 3 C(s) 4 Fe(s) + 3 CO 2 (g) , H = 462 kJ , S = 558 J K 1 . Calcu- late the equilibrium constant for this reaction at 525 C....
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This note was uploaded on 10/20/2011 for the course CH 302 taught by Professor Holcombe during the Fall '07 term at University of Texas at Austin.

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Homework 1-solutions - alexander (jra2623) Homework 1...

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