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# ism_ch17 - Chapter 17 Phases and Phase Changes Answers to...

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360 Chapter 17 Phases and Phase Changes Answers to Even-numbered Conceptual Questions 2. Carbon is monatomic, whereas oxygen is diatomic. Therefore, one mole of oxygen has twice as many atoms as one mole of carbon. 4. The bubble wrap is more effective on a warm day because the air pressure within the bubbles will be greater, leading to more effective cushioning. At low temperature, the bubbles are almost flat. 6. If the temperature of the air in a house is increased, and the amount of air in the house remains constant, it follows from the ideal-gas law that the pressure will increase as well. 8. Yes. If the pressure and volume are changed in such a way that their product remains the same, it follows from the ideal-gas law that the temperature of the gas will remain the same. If the temperature of the gas is the same, the average kinetic energy of its molecules will not change. 10. Both types of molecules have the same average kinetic energy, because they experience the same temperature. Since the oxygen molecules are more massive, however, it follows that their rms speed is less than the rms speed of the nitrogen. In general, heavier molecules move more slowly for a given temperature. 12. The ratio of oxygen to nitrogen decreases with increasing altitude. The reason is that oxygen molecules move more slowly than nitrogen molecules, on average, and are therefore unable to rise as high above the ground as nitrogen molecules. 14. Airplanes can have a difficult time taking off from high-altitude airports because the air is thin, and provides less lift than air at sea level. When the air is cool, however, its density is greater than when it is warm. Therefore, taking off in the morning or evening will provide the airplane with more lift – which can be very important at high altitude. 16. If the absolute temperature of an ideal gas is doubled, the average kinetic energy of its molecules doubles as well. Recall that kinetic energy depends on speed squared, however. It follows, then, that the average speed of the molecules increases by a factor less than 2; in fact, the speed increases by a factor of the square root of 2. 18. The change in length is inversely proportional to the cross sectional area, as we see in Equation 17-17. The solid rod has the greater effective cross-sectional area – since the hollow part of the other rod doesn’t resist compression. Therefore, the hollow rod has the greater change in length. 20. No. The temperature at which water boils on a mountain top is less than its boiling temperature at sea level – due to the low atmospheric pressure on the mountain. Therefore, if the stove is barely able to boil water on the mountain, it will not be able to boil it at sea level, where the required temperature is greater.

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