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 – fnd 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 substance’s 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. 1.
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