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Homework 1-solutions

# Homework 1-solutions - tran(pt4954 Homework 1 sutclie(51045...

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tran (pt4954) – 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 10.0points If Δ G rxn is positive, then the forward reaction is (spontaneous / nonspontaneous) and K is (less / greater) than one. 1. nonspontaneous; less correct 2. nonspontaneous; greater 3. spontaneous, greater 4. spontaneous, less 5. None of these; Δ G is not directly related to K . Explanation: A positive Δ G rxn (standard reaction free energy) denotes an endothermic reation, which is nonspontaneous. Also, Δ G rxn = - RT ln K , so a positive Δ G rxn would result in a K that is between the values of zero and one. 002 10.0points Which combination of Δ G and K is im- possible? 1. Δ G = 16 J, K = 635 correct 2. Δ G = - 37 . 4 kJ, K = 3 . 57 × 10 6 3. Δ G = 18 . 5 J, K = 0 . 993 4. Δ G = 86 . 4 kJ, K = 7 . 31 × 10 16 5. Δ G = - 72 J, K = 1 . 03 Explanation: If Δ G is positive, K must be less than 1; if Δ G is negative, K must be greater than 1. Also, if Δ G is small (compared to RT), then K will be close to 1, and if Δ G is large, K will be much smaller or greater than 1. 003 10.0points When Δ G 0 is calculated for a proposed reac- tion, the process being described is 1. any mixture of reactants converted to equilibrium mixture. 2. 100% reactants converted to equilibrium mixture. 3. any mixture of reactants and products converted to equilibrium mixture. 4. 100% reactants converted to 100% prod- ucts. correct Explanation: Δ G 0 = Δ G 0 final - Δ G 0 initial = Δ G 0 products - Δ G 0 reactants 004 10.0points Note: The ’reaction progress’ axis reads from all reactants (far L) to all products (far R) The figure represents a reaction at 298 K. G A B C D E rxn progress Based on the figure, the standard reaction is 1. nonspontaneous. 2. spontaneous. correct Explanation: Δ G is negative (point E is lower free en- ergy than point A), so the standard reaction is spontaneous. 005 10.0points A gas-phase reaction has K p = 3 . 99 × 10 20 at 25 C. Calculate Δ G 0 for this reaction. Correct answer: - 117 . 549 kJ / mol rxn. Explanation:

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tran (pt4954) – Homework 1 – sutcliffe – (51045) 2 K p = 3 . 99 × 10 20 T = 25 C + 273 = 298 K Δ G 0 = - RT ln K p = - (8 . 314 J / mol · K) (298 K) × ln ( 3 . 99 × 10 20 ) = - 117 . 549 kJ / mol rxn 006 10.0points Consider the reaction 2 Fe 2 O 3 (s) + 3 C(s) 4 Fe(s) + 3 CO 2 (g) , Δ H = 462 kJ , Δ S = 558 J · K 1 . Calcu- late the equilibrium constant for this reaction at 525 C.
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Homework 1-solutions - tran(pt4954 Homework 1 sutclie(51045...

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