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2010 Exam 2 Key - Name Section Number Chemistry 1314 Honors...

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2010 Exam 2 Key

2010 Exam 2 Key - Name Section Number Chemistry 1314 Honors...

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N a m e Section Number Chemistry 1314 Honors Midterm Exam #2 October 6, 2010 This exam is closed book, notes, papers, etc. You may use a calculator. If you need a physical constant or unit conversion factor that is not provided, please ask. This exam must represent your own work. Constants and Conversion Factors: N A = 6.022 x 10 23 particles/mol R = 8.20578 x 10 -2 (atm L)/(mol K) h = 6.62607 x 10 -34 J s c = 2.99792 x 10 8 m/s m e = 9.10939 x 10 -31 kg 1 J = 1 kg m 2 s -2 van der Waals equation: () nRT nb V V a n p = + 2 2 Rydberg equation: = 2 2 2 1 1 1 1 n n λ , =1.096776 x 10 7 m -1 Scores: 1. / 20 (25 possible) 2. a. / 10 b. / 10 3. a. / 9 b. / 6 c. / 5 4. / 20 (25 possible) 5. / 20 (25 possible) Total: / 100 (115 possible)
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CHEM 1314 H Midterm Exam #2, 2010 Page 2 1. In terms of the postulates and conclusions of the kinetic molecular theory of gases, give a brief molecular interpretation of each of the following experimental observations: a. The volume of a gas at fixed pressure increases proportionally with the temperature. b. For a fixed volume and temperature, the total pressure of a mixture of one mole of oxygen and one mole of nitrogen is equal to the total pressure of two moles of nitrogen. c. The temperature of a gas can be raised by heating it with a flame or by stirring it with a blender. d. For a fixed volume and temperature, the pressure exerted by a mole of gas with strong intermolecular attractions is significantly less than the pressure exerted by a mole of gas with weaker intermolecular attractions. e. One mole of gas A occupies the same volume as one mole of gas B (at the same temperature and pressure), even if the molecules of compounds A contain many more atoms than do the molecules of compound B. Increasing T increases average speed, resulting in greater force of collisions of particles with walls. If resisting pressure is fixed, the pressure due to collisions will push back container walls, thus expanding volume. Force generated by a particle colliding with a wall depends on kinetic energy, not mass or chemical character. Thus, pressure of two moles is independent of what molecules those particles are, because there are no interactions. Temperature is a measure of kinetic energy. Molecules can be accelerated thermally or mechanically. When molecules attract each other, they experience a decelerating force as they approach the walls. This lowers the force of impact, lowering the observed pressure. 5 points each In an ideal gas, the particles are at great distances from one another. At these distances, the sizes of the molecules are insignificant, so differences in sizes are irrelevant.
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CHEM 1314 H Midterm Exam #2, 2010 Page 3 2. Assuming ideal gas behavior, answer the following questions by performing appropriate calculations. a.
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