# Exam 3 - Version 440 – Exam 3 – Laude –(53755 1 This...

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Unformatted text preview: Version 440 – Exam 3 – Laude – (53755) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 6.0 points If an MP3 player does 200 kJ of work and releases 100 kJ of heat, what is the change in internal energy for the MP3 player? 1. 300 kJ 2. 100 kJ 3.- 300 kJ correct 4.- 100 kJ Explanation: Δ U = q + w =- 100 kJ +- 200 kJ =- 600 kJ 002 6.0 points You observe that carbon dioxide sublimes. Which of the following statements about the signs of this process is/are true? I) Work (w) is positive. II) Heat (q) is negative. III) Change in Gibbs free energy (Δ G ) is pos- itive. IV) Change in entropy (Δ S ) is positive. 1. IV only correct 2. I only 3. III and IV 4. I and II 5. II and III 6. I, II and III Explanation: Sublimation results in a significant increase in the volume of the system, allowing it to do work on its surroundings, i.e. the pressure-volume work function is negative. Sublimation is also an endothermic process, making heat positive. Since the process de- scribed ”happens” as a given in the problem, the change in free energy must be negative. Change in entropy must be positive since a solid is becoming a gas. 003 6.0 points Which of the following is not a definition of internal energy or change in internal energy? 1. A measure of the spontaneity of a reac- tion. correct 2. The total energy content of a system. 3. A measure of the change in heat of a system at constant volume. 4. The sum of heat (q) and work (w). Explanation: Gibbs free energy is a measure of the spon- taneity of a reaction. All of the other state- ments are mathematical identities describing internal energy or prose restatements of the same. 004 6.0 points Based on enthalpy of formation data, cal- culate Δ H for the reaction: 3H 2 O 2 (l) + 2Fe(s) ←→ 3H 2 O(l) + Fe 2 O 3 (s) 1.- 992 kJ · mol − 1 2.- 1 , 118 kJ · mol − 1 correct 3. 1 , 118 kJ · mol − 1 4. 992 kJ · mol − 1 Explanation: Δ H rxn = ΣΔ H f,products + ΣΔ H f,reactants = (3 · Δ H f,H 2 O ( l ) + Δ H f,Fe 2 O 3 ( s ) )- (3 · Δ H f,H 2 O 2 ( l ) + 2 · Δ H f,Fe ( s ) ) Version 440 – Exam 3 – Laude – (53755) 2 = (3 ·- 285 . 83 kJ · mol − 1 +- 824 . 2 kJ · mol − 1 )- (3 ·- 187 . 78 kJ · mol − 1 + 2 · 0) =- 1 , 118 kJ · mol − 1 005 6.0 points If a system at 273 ◦ C absorbs 1000 J of heat, what is its change in entropy? 1. 1 . 83 J · K − 1 correct 2.- 1 . 83 J · K − 1 3. 3 . 66 J · K − 1 4.- 3 . 66 J · K − 1 Explanation: Heat absorbed by a system will increase its entropy by an amount equal to q/T , in this case 1000J / 546K = 1 . 83 J · K − 1 . 006 6.0 points Which of the following would experience the smallest increase in temperature if 1 kJ of heat were added to it?...
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## This note was uploaded on 06/06/2010 for the course CH 301 taught by Professor Fakhreddine/lyon during the Fall '07 term at University of Texas.

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Exam 3 - Version 440 – Exam 3 – Laude –(53755 1 This...

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