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Unformatted text preview: 19 Temperature CHAPTER OUTLINE 19.2 Thermometers and the Celsius Temperature Scale 19.3 The Constant-Volume Gas Thermo- meter and the Absolute Temperature Scale 19.4 Thermal Expansion of Solids and Liquids 19.5 Macroscopic Description of an Ideal Gas ANSWERS TO QUESTIONS Q19.1 Two objects in thermal equilibrium need not be in con- tact. Consider the two objects that are in thermal equili- brium in Figure 19.1(c). The act of separating them by a small distance does not affect how the molecules are moving inside either object, so they will still be in thermal equilibrium. Q19.2 The coppers temperature drops and the water tempera- ture rises until both temperatures are the same. Then the metal and the water are in thermal equilibrium. Q19.3 The astronaut is referring to the temperature of the lunar surface, specifi cally a 400 F difference. A thermometer would register the temperature of the thermometer liquid. Since there is no atmo- sphere in the moon, the thermometer will not read the temperature of some other object unless it is placed into the lunar soil. *Q19.4 Answer (e). The thermometer works by differential expansion. As the thermometer is warmed the liquid level falls relative to the tube wall. If the liquid and the tube material were to expand by equal amounts, the thermometer could not be used. *Q19.5 Answer (b). Around atmospheric pressure, 0 C is the only temperature at which liquid water and solid water can both exist. *Q19.6 Mentally multiply 93 m and 17 and 1 / (1 000 000 C) and say 5 C for the temperature increase. To simplify, multiply 100 and 100 and 1 / 1 000 000 for an answer in meters: it is on the order of 1 cm, answer (c). Q19.7 The measurements made with the heated steel tape will be too shortbut only by a factor of 5 10 5 of the measured length. Q19.8 (a) One mole of H 2 has a mass of 2.016 0 g. (b) One mole of He has a mass of 4.002 6 g. (c) One mole of CO has a mass of 28.010 g. Q19.9 PV = nRT predicts V going to zero as T goes to zero. The ideal-gas model does not apply when the material gets close to liquefaction and then turns into a liquid or solid. The molecules start to interact all the time, not just in brief collisions. The molecules start to take up a signifi cant portion of the volume of the container. 497 13794_19_ch19_p497-518.indd 497 13794_19_ch19_p497-518.indd 497 12/20/06 7:30:31 PM 12/20/06 7:30:31 PM *Q19.10 Call the process isobaric cooling or isobaric contraction. The rubber wall is easy to stretch. The air inside is nearly at atmospheric pressure originally and stays at atmospheric pressure as the wall moves in, just maintaining equality of pressure outside and inside. The air is nearly an ideal gas to start with, and stays fairly idealfairly far from liquefactioneven at 100 K. The water vapor liquefi es and then freezes, and the carbon dioxide turns to snow, but these are minor con- stituents of the air. Thus as the absolute temperature drops to 1 3 of its original value the volume...
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- Spring '10