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Unformatted text preview: phan (dtp377) – Homework 1 – sutcliffe – (51045) 1 This printout should have 20 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points If Δ G ◦ rxn is positive, then the forward reaction is (spontaneous / nonspontaneous) and K is (less / greater) than one. 1. None of these; Δ G is not directly related to K . 2. spontaneous, less 3. spontaneous, greater 4. nonspontaneous; less correct 5. nonspontaneous; greater 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 10.0 points Which combination of Δ G ◦ and K is im possible? 1. Δ G ◦ = 79 . 5 J, K = 8 . 46 × 10 13 correct 2. Δ G ◦ = 31 . 8 kJ, K = 2 . 69 × 10 − 6 3. Δ G ◦ = 92 . 6 J, K = 1 . 04 4. Δ G ◦ = 101 kJ, K = 4 . 94 × 10 17 5. Δ G ◦ = 71 . 8 J, K = 0 . 971 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 10.0 points When Δ 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. 100% reactants converted to equilibrium mixture. 3. 100% reactants converted to 100% prod ucts. correct 4. any mixture of reactants converted to equilibrium mixture. Explanation: Δ G = Δ G final Δ G initial = Δ G products Δ 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: Δ G ◦ is negative (point E is lower free en ergy than point A), so the standard reaction is spontaneous. 005 10.0 points A gasphase reaction has K p = 5 . 62 × 10 20 at 25 ◦ C. Calculate Δ G for this reaction. Correct answer: 118 . 398 kJ / mol rxn. Explanation: phan (dtp377) – Homework 1 – sutcliffe – (51045) 2 K p = 5 . 62 × 10 20 T = 25 ◦ C + 273 = 298 K Δ G = RT ln K p = (8 . 314 J / mol · K) (298 K) × ln ( 5 . 62 × 10 20 ) = 118 . 398 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) , 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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 Fall '10
 McCord
 Chemistry, Critical Point, pH, Reaction, Vapor pressure, Phan

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