practice_exam_MidTerm 1 Problems

practice_exam_MidTerm 1 Problems - PRACTICE PROBLEMS FOR...

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PRACTICE PROBLEMS FOR CHEM452 ©2010 Sarah L. Keller Here’s how to assemble your own practice exam: 1) Print out random pages until you have about 70 points worth of problems assembled. (How did I come up with 70? Well, from 2003 to 2008, the midterms that I gave at week 4 in Chem452 were worth 73, 73, 68, 75, 67, and 63, and 69 points. The average is about 70 points.) 2) The first page of the exam, which will contain equations you’ll need, and a table of physical constants for water, will be posted on the Chem452 website. Print them out. 3) Staple your first page, your table of constants, and your pages with questions together. Now you have a practice exam. Take it all to a quiet room and see what you can do in 50 minutes. Use a non-graphing calculator that does not do calculus. 4) Notice that you probably won’t finish. That’s perfectly fine. Most students don’t. 5) Compare your answers with those of your friends. (Yes, I also have the answers. No, you can’t have them from me.) 6) Want more practice? Do it again.

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Sarah L. Keller © 2008 NAME = superdome 3) The Superdome became famous as an emergency shelter during Hurricane Katrina in 2005. Today it houses football games. It takes 2 DAYS to prime the air conditioning for a sold-out New Orleans Saints game. Assume the dome’s doors are sealed tightly shut on a balmy fall day at 82˚F. After 2 days the air inside the dome is 55˚F. Assume there were no air leaks, and no heat loss from the air to the building (both are unrealistic). The dome is a cylinder 82.3 meters tall (~27 stories), and 210 meters in diameter, at 1 meter above sea level. You may assume air is an ideal gas with C V = 5/2R. Describe any other reasonable assumptions you make. (20 points total) Photo from http://www.greatbuildings.com/buildings/Louisiana_Superdome.html i) For the situation above, circle all the true statements from the choices below. a) P-V work of air = - q b) P-V work of air = q c) ± H = q d) ± E = q ii) Find the change of internal energy and the change of enthalpy of the air inside the superdome. place your answer here: place your answer here: Problem continued on the next page…
Sarah L. Keller © 2008 Continued… iii) If electricity costs about 10 cents per kiloWatt-hour (and one Watt = 1J/s), how much does it cost to cool the Louisiana Superdome for one game (in dollars)? place your answer here: iv) The building’s air conditioners use energy from the electrical grid to cool the air (albeit rather inefficiently). Air conditioner efficiency = |(Thot – Tcold)/Tcold|. Let’s assume that there is a device (called a rectifier) between the plug and the air conditioners that turns the standard outlet’s AC voltage into a direct voltage of 80V. How many amps of current did the air conditioners draw while cooling the Superdome? place your answer here:

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Sarah L. Keller © 2008 NAME: Hadley cell 5) This year hurricanes pummeled the East Coast of the U.S., so here is a question about the circulation of air above the earth.
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This note was uploaded on 03/04/2010 for the course CHEM CHEM 452 taught by Professor Robinson during the Winter '09 term at University of Washington.

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practice_exam_MidTerm 1 Problems - PRACTICE PROBLEMS FOR...

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