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Assigned problems _2

# Assigned problems _2 - is equivalent to 1 joule per second...

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Chemistry 2080 Spring 2009 Problem Set #2 - due date: Friday February 12th at 2 pm Name:________________ Lab TA Name:__________________ Lab Day/Time:______________________ 1) In 2001 a Pastor was clearing icicles off the edge of the roof of his church when he dislodged an ice-dam weighing about half a ton. The falling ice-dam plus the remains of the icicle broke his collar bone and crushed his foot. His leg had to be amputated and two weeks later, while recuperating he died of a blood clot in his lung. Details can be seen here: http://www.cdc.gov/niosh/FACE/stateface/mi/01mi006.html Some people try to avoid ice-dam formation by using electrically-heated tape on the edge of the roof, but the better solution is to ventilate the attic with cold air from the outside, and to minimize the penetration of warm air into the attic from the heated living space below. However, let’s see what we can do with some electricity. Remember that 1 watt

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Unformatted text preview: is equivalent to 1 joule per second, and watts are given by amps times volts. Suppose you have a lump of ice that weighs 1,100 lbs, and it starts at -10°C. How much electricity would it take in kilowatt-hours to just melt all of the ice and produce water still at 0°C. Assume that all of the heat goes to warm the ice and then melt it. Note that the specific heat of ice is about 2.05 J/g.°C and the heat of fusion for water is 6.01 kJ/mol at 0°C. 2) Use Hess’s Law to find Δ H rxn for the reaction: 3C(s) + 4H 2 (g) ––––––> C 3 H 8 (g) (i.e. propane) Given the following reactions that have known values of Δ H: C 3 H 8 (g) + 5O 2 (g) ––––––> 3CO 2 (g) + 4H 2 O(g) Δ H = – 2043 kJ C(s) + O 2 (g) –––––––> CO 2 (g) Δ H = – 393.5 kJ 2H 2 (g) + O 2 (g) –––––––> 2H 2 O(g) Δ H = – 483.6 kJ...
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