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# hw7 - CHM 2047 This assignment is due Friday Oct 14 in...

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Unformatted text preview: CHM 2047 This assignment is due Friday, Oct. 14, in class. 1. Kotz, Ch. 12, Problem 84. 2. Kotz, Ch. 12, Problem 86. 3. Kotz, Ch. 12, Problem 90. 4. Kotz, Ch. 12, Problem 94. 5. Kotz, Ch. 12, Problem 104. Homework 7 6. The earth is approximately a sphere of radius 6370 km. Taking the average barometric pressure on the earth’s surface to be 730 mm (Hg), estimate the total mass of the earth’s atmosphere. 7. After a ﬂood ﬁlls a basement to a depth of 9.0 feet and completely saturates the surrounding earth, the owner buys an electric pump and quickly pumps the water out of the basement. Suddenly, a basement wall collapses, the structure is severely damaged, and mud oozes in. Explain this event by estimating the diﬀerence between the outside pressure at the base of the basement walls and the pressure inside the drained basement. Assume that the mud has a density of 4.9 g/cm3 . Report the answer both in atmospheres and in pounds per square inch. 8. Baseball reporters say that long ﬂy balls that would have carried for home runs in July “die” in the cool air of October and are caught. The idea behind this observation is that a baseball carries better when the air is less dense. Dry air is a mixture of gases with an eﬀective molar mass of 29.0 g/mol. (a) Compute the density of dry air on a July day when the temperature is 95.0◦ and the pressure is 1.00 atm. (b) Compute the density of dry air on an October evening when the temperature is 50.0◦ and the pressure is 1.00 atm. (c) Suppose that the humidity on the July day is 100%, so the air is saturated with water vapor. Is the density of this hot, moist air less than, equal to, or greater tan the density of the hot, dry air in July? In other terms, does high humidity favor the home run? 9. A sample of limestone (calcium carbonate, CaCO3 ) is heated at 950 K until it is completely converted to calcium oxide (CaO) and CO2 . The CaO is then all converted to calcium hydroxide by addition of water to yield 8.47 g of Ca(OH)2 . Calculate the volume of CO2 produced in the ﬁrst step, assuming it to be an ideal gas at 950 K and a pressure of 0.976 atm. 10. A thermos bottle has an evacuated space between its inner and outer walls to diminish the rate of transfer of thermal energy to or from the bottle’s contents. For good insulation the mean free path of the residual gas (air; average molecular mass = 29 g/mol) should be at least ten times the distance between the inner and outer walls, which is about 1.0 cm. What should be the maximum residual gas pressure in the evacuated space if T = 300 K? Assume an average diameter of d = 3.1 × 10 −10 m for the molecules in the air. Please note two additional questions on the following page. 2 !" #\$ & " () !" +, , ! * , . , (/*( +++ ' % & ! /0 1 ' ...
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