SolutionEXAM 1_pdf - Version 096 Exam 1 Fakhreddine(52395 This print-out should have 25 questions Multiple-choice questions may continue on the

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Version 096 – Exam 1 – Fakhreddine – (52395) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – fnd all choices be±ore answering. 001 12.0 points specifc heat o± H2O(l) = 4.18 J/g.C, enthalpy o± evaporation o± water = 2.26 x 103 J/g; spe- cifc heat o± H2O (g) = 2.03 J/g.C; enthalpy o± ±usion o± ice = 334.0 J/g; and specifc heat o± H2O(s) = 2.09 J/g.C Consider an insulated system containing 150 g o± liquid water and 150 g o± ice at equilibrium under atmospheric pressure. A total o± 17 g o± steam at 110 C is admitted to the system. What is the phase composition and temperature when equilibrium is reestab- lished? 1. 300 g o± water and 17 g o± ice at 0 C 2. 317 g o± water at 3.2 C 3. 317 g o± water at 6.8 C 4. 304 g o± water and 13 g o± ice at 0 C correct 5. 310 g o± water and 7 g o± ice at 0 C 6. 317 g o± water at 15.3 C Explanation: 002 12.0 points How many grams o± methanol (CH 3 OH) are needed to lower the ±reezing point o± 400 mL o± water by 2.5 C? ( K f water = 1 . 86 C/molality) 1. 9.71 2. 17.2 correct 3. 12.8 4. 21.8 5. 18.3 Explanation: K f H 2 O = 1 . 86 C /m V water = 400 L FP depression = 2.5 C Δ T f = K f · m m = Δ T f K f = 2 . 5 C 1 . 86 C /m = 1 . 344 m m H 2 O = 400 mL × 1 . 00 g mL × 10 3 kg g = 0 . 4 kg H 2 O m = n CH 3 OH kg water = g CH 3 OH MW CH 3 OH kg water g CH 3 OH = m (kg water) (MW CH 3 OH ) = p 1 . 344 mol CH 3 OH kg water P × (0 . 400 kg water) × p 32 . 0 g CH 3 OH mol CH 3 OH P = 17 . 2 g CH 3 OH 003 5.0 points Dissociation o± a solid is aided by 1. None o± these is correct. 2. strong binding in the solid and weak solvent-solute interaction. 3. strong interaction between solvent molecules. 4. weak binding o± species in the solid and strong interactions between the solvent and solute. correct Explanation: Weak intermolecular ±orces in the solute ±acilitate separation o± its particles and strong attractive ±orces between solute and solvent ±acilitate dissociation o± a solid. 004 12.0 points Methanol (CH 3 OH) and ethanol (C 2 H 5 OH) are common organic solvents. The vapor pressures o± pure methanol and pure ethanol
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Version 096 – Exam 1 – Fakhreddine – (52395) 2 at 25 C are 122 . 7 torr and 58 . 9 torr, respec- tively. If the mole fraction of CH 3 OH in the mixture of the two solvents at 25 C is 0 . 2, what is the mole fraction of C 2 H 5 OH in the vapor phase that is in equilibrium with the liquid mixture? 1. 0 . 508 2. 0 . 348 3. 0 . 658 correct 4. 0 . 743 5. 0 . 428 6. 0 . 828 7. 0 . 591 Explanation: P methanol = 122 . 7 torr χ methanol = 0 . 2 P ethanol = 58 . 9 torr χ ethanol = 1 - χ methanol = 1 - 0 . 2 = 0 . 8 . P
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This note was uploaded on 04/08/2009 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas at Austin.

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SolutionEXAM 1_pdf - Version 096 Exam 1 Fakhreddine(52395 This print-out should have 25 questions Multiple-choice questions may continue on the

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