# hw 5 - Garg Pallavi Homework 5 Due 2:00 am Inst Donna C...

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Garg, Pallavi – Homework 5 – Due: Nov 28 2007, 2:00 am – Inst: Donna C Lyon 1 This print-out should have 35 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. This HW assignment is due Tuesday, November 27 by 2:00AM. DO NOT WAIT UNTIL THE LAST HOUR TO TURN IN YOUR HOMEWORK ANSWERS. KEEP UP WITH THE MATERIAL BY ANSWER- ING QUESTIONS AS THEY ARE COV- ERED IN CLASS. 001 (part 1 of 1) 10 points What is the total motional contribution to the molar internal energy of gaseous BF 3 ? 1. 3 R T correct 2. 2 . 5 R T 3. R T 4. 3 . 5 R T 5. 1 . 5 R T Explanation: 002 (part 1 of 1) 10 points A CD player and its battery together do 500 kJ of work, and the battery also releases 250 kJ of energy as heat, and the CD player re- leases 50 kJ as heat due to friction from spin- ning. What is the change in internal energy of the system, with the system regarded as the battery alone? Assume that the battery does 500 kJ of work on the CD player, which then does the same amount of work on the surroundings. 1. - 800 kJ 2. +200 kJ 3. - 750 kJ correct 4. - 50 kJ 5. - 700 kJ Explanation: 003 (part 1 of 1) 10 points The combustion of one mole of ethanol (C 2 H 5 OH( )) to produce carbon dioxide and gaseous water has Δ H r = - 1235 kJ · mol - 1 at 298 K. What is the change in internal en- ergy for this reaction? 1. - 1240 kJ · mol - 1 correct 2. - 1230 kJ · mol - 1 3. - 1237 kJ · mol - 1 4. - 1223 kJ · mol - 1 5. - 1247 kJ · mol - 1 Explanation: 004 (part 1 of 1) 10 points For the ethylene combustion reaction C 2 H 4 + 3 O 2 2 CO 2 + 2 H 2 O , assume that all reactants and products are gases. For one mole of ethylene, estimate the magnitude of the P Δ V work done at constant pressure and determine whether the work is done on the system or on the surroundings. Assume a room temperature of 300 K. 1. 5.0 kJ/mole of P Δ V work is done on the surroundings. 2. 2.5 kJ/mole of P Δ V work is done on the surroundings. 3. There is no P Δ V work done on the sys- tem. correct 4. 2.5 kJ/mole of P Δ V work is done on the system. 5. 5.0 kJ/mole of P Δ V work is done on the system. Explanation: Work involves a change of energy in which a body is moved through a distance d against

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Garg, Pallavi – Homework 5 – Due: Nov 28 2007, 2:00 am – Inst: Donna C Lyon 2 some force f : w = d × f . When the volume is constant, there is no movement through a distance ( d = 0 and w = 0), so w = - P Δ V = 0. 4 moles of gaseous reactants form 4 moles of gaseous products; therefore there is no volume change. Δ V = 0 , w = - P Δ V = 0. 005 (part 1 of 1) 10 points A 1.00 g sample of n -hexane (C 6 H 14 ) under- goes complete combustion with excess O 2 in a bomb calorimeter. The temperature of the 1502 g of water surrounding the bomb rises from 22.64 C to 29.30 C. The heat capacity of the calorimeter is 4042 J/ C. What is Δ U for the combustion of n -C 6 H 14 ? One mole of n -C 6 H 14 is 86.1 g. The specific heat of water is 4.184 J / g · C.
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