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Unformatted text preview: Kang, Danby Homework 2 Due: Sep 14 2007, 10:00 pm Inst: Walker 1 This print-out should have 22 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. The due time is Central time. CHAPTER 8 001 (part 1 of 1) 2 points On a relative basis, the weaker the intermolec- ular forces in a substance 1. the larger its molar heat capacity as a liquid. 2. the higher its melting point. 3. the more it deviates from the ideal gas law. 4. the greater its vapor pressure at a partic- ular temperature. correct 5. the larger its heat of vaporization. Explanation: Weak intermolecular forces suggest that it is easy to cause molecules of the substance to be pulled away from each other. Thus it will take a relatively low temperature to both melt and boil the substance. Weaker inter- molecular forces also mean that the substance will have a relatively high vapor pressure at a given temperature (which would cause the compound to boil at a lower temperature, since the normal boiling point would occur when the substances vapor pressure reaches 760 torr.) 002 (part 1 of 1) 2 points Which of the following is expected to boil at the highest temperature? 1. C 3 H 8 2. CH 4 3. C 5 H 12 correct 4. C 4 H 10 5. C 2 H 6 Explanation: The boiling point tends to increase with increasing molecular weight. C 5 H 12 has the biggest MW, so it should boil at the highest temperature. 003 (part 1 of 1) 2 points Consider the following statements: I) The vapor pressure of ethyl alcohol in- creases as temperature increases. II) Liquids with low molecular weight ex- hibit relatively high vapor pressures, liq- uids with high molecular weight show relatively low vapor pressures, and solids do not have vapor pressures. III) A liquid boils at a higher temperature at sea level than on top of a mountain. IV) The temperature of boiling water inside a pressure cooker at sea level is above 100 C. Which response contains all of the TRUE statements, and no others? 1. II and IV only 2. III only 3. I and IV only 4. I, III, and IV only correct 5. I and II only Explanation: Solids can have vapor pressures. CO 2 sub- limes (s g) and therefore has a vapor pres- sure. When temperature increases, molecules have greater energy to overcome intermolec- ular forces/bonds and will therefore have in- creased vapor pressures. Atmospheric pressure is greater at sea level. Molecules require more energy (higher tem- peratures) to vaporize when pressure is high. 004 (part 1 of 1) 5 points Liquid metallic zinc (Zn) has a vapor pressure of 40 torr at 673 C and 100 torr at 736 C. Kang, Danby Homework 2 Due: Sep 14 2007, 10:00 pm Inst: Walker 2 Predict the normal boiling point of zinc....
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