#Chem 161-2007 Chapter 5-Gases practice problems - CHEM...

#Chem 161-2007 Chapter 5-Gases practice problems
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CHEM 161-2007 CHAPTER 5 - GASES PRACTICE PROBLEMS DR. ED TAVSS Pressure Gas laws Reaction stoichiometry Partial pressure (mixtures of gases) Kinetic molecular theory/Effusion and Diffusion/Real gases
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PRESSURE CHEM 161-2006 EXAM II GASES PRESSURE 14. In the above drawing, the value of h, the height of the liquid in the tube above the liquid in the beaker, would depend on which of the following? X. Density of the liquid Y. Cross sectional area of the tube Z. Atmospheric pressure (a) Z only (b) Y and Z only (c) X and Y only (d) X and Z only (e) X, Y, and Z This is a barometer. The liquid is held in the tube by atmospheric pressure. If the atmospheric pressure is exactly 1 atmosphere (14.7 lb/in 2 ), then the liquid would have to exert a pressure of 14.7 lb/in 2 . (X) If the liquid was, let’s say, less dense, then it would have to be a greater height to exert a pressure of 14.7 lb/in 2 . If the liquid was more dense then it would have to be a shorter height.
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(Y) The cross sectional area of the tube is irrelevant, since the pressure (14.7 lb/in 2 ) would be the same regardless of the cross-sectional area. (Z) If the atmospheric pressure decreased, then the height would decrease because it would require less liquid to be equal to a lower pressure. If the atmospheric pressure increased, then the height would need to increase. 14 Chem 161-2005 Hourly Exam II Chapter 5 - Gases Pressure Which of the following is a unit of pressure? A. 3 cm g B. 3 m kg C. pounds D . 2 m N E . 2 cm g Pressure is force per unit area. A is force per unit volume. B is force per unit volume C is force D is force per unit area. E is force per unit area. The acceptable answer is “D”. I disagree. “E” should also be acceptable. Some faculty members consider “N” as force, and “g” as mass. Since pressure is force per unit area then only “D” is allowed. In my opinion this is nit-picking semantics. 15. Chem 162-2004 Hourly exam II Chapter 5 - Gases
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Mercury, rather than water, is used as a liquid in barometers because: A. Mercury is more sensitive to pressure changes than water. B. Mercury is safer. C. Pressure is measured in mm of mercury. D . Mercury is denser. E. Mercury is metallic. A barometer works by the pressure of the air (e.g., 1 atmosphere) being equal and opposite to the pressure exerted by the liquid in the barometer. The pressure exerted by the liquid in the barometer is due to its height and its mass. For mercury, this height is 760 mm. Since water has a density 13.6 times less than the density of mercury, it would require a height of 760 mm x 13.6 = 10336 mm = 33.9 feet, and therefore would be too cumbersome to be useful. 2.
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