Exam 4-solutions

# Exam 4-solutions - Version 103 Exam 4 sutcliffe (52380) 1...

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Unformatted text preview: Version 103 Exam 4 sutcliffe (52380) 1 This print-out should have 24 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Consider the following specific heats: cop- per, 0.384 J/g C; lead, 0.159 J/g C; water, 4.18 J/g C; glass, 0.502 J/g C. If the same amount of heat is added to identical masses of each of these substances, which substance at- tains the highest temperature? (Assume that they all have the same initial temperature.) HINT: Think before you calculate very lit- tle calculation is needed to answer this ques- tion! 1. glass 2. lead correct 3. water 4. copper Explanation: 002 10.0 points A battery does 35 kJ of work driving an elec- tric motor. The battery also releases 7 kJ of heat. What is the change in internal energy of the system? Assume the motor is not part of the system. 1.- 35 kJ 2. +28 kJ 3.- 28 kJ 4. +42 kJ 5.- 42 kJ correct Explanation: U = q + w =- 7 kJ + (- 35) kJ =- 42 kJ . 003 10.0 points A drinking mug made from Pyrex glass is placed in the freezer and chilled to- 10 C. It is then removed from the freezer and 200 mL of cool water at 12 C is poured inside. What will be the final temperature of the resulting system, assuming NO heat is exchanged with the surroundings? The specific heat of Pyrex is 0 . 753 J / g C and the mass of the mug is 455 g. Recall that the density of water is 1 g/mL. 1. 3.15 C 2. 0.644 C 3. 5.60 C correct 4. 16.09 C Explanation: T m =- 10 C V w = 200 mL T w = 12 C C m = 0 . 753 J / g C m m = 455 g w = 1 g/mL c m = 0 . 753 J / g C The mass of the water is m w = (1 g / mL)(200 mL) = 200 g . Heat flows from the water into the mug. Both end up at the same temperature (assum- ing no heat exchange with the surroundings), so q m =- q w m m C m T m =- m w C w T w m m C m ( T f- T m ) =- m w C w ( T f- T w ) T f = m m C m T m + m w C w T w m m C m + m w C w Since m m C m + m w C w = (455 g)(0 . 753 J / g C) + (200 g)(4 . 18 J / g C) = 1178 . 62 J / C , T f = (455 g)(0 . 753 J / g C)(- 10 C) 1178 . 62 J / C + (200 g)(4 . 18 J / g C)(12 C) 1178 . 62 J / C = 5 . 60476 C . Version 103 Exam 4 sutcliffe (52380) 2 004 10.0 points What is the entropy at T = 0 K for one mole of chloroform (CHCl 3 ), which can orient four ways? 1. 1.38 J/K 2.- 11 . 5 J/K 3. 11.5 J/K correct 4. 1 . 9 10 23 J/K 5. 0 J/K Explanation: 005 10.0 points A process CANNOT be spontaneous if 1. it is endothermic and there is a decrease in disorder. correct 2. it is endothermic and there is an increase in disorder....
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## This note was uploaded on 10/20/2011 for the course CH 301 taught by Professor Fakhreddine/lyon during the Fall '07 term at University of Texas at Austin.

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Exam 4-solutions - Version 103 Exam 4 sutcliffe (52380) 1...

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