Chem2080_2009_Prelim1_key

Chem2080_2009_Prelim1_key - Page 1 of 6 Chemistry 2080 -...

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Page 1 of 6 Chemistry 2080 - Spring 2009 Prelim #1 Tuesday February 24, 7:30 to 9:00 pm KEY Name: _____________________________________ CU ID: ____________________ Last First M.I. Lab: _______________________________ Lab TA Name: __________________ Day Time Instructions: Answer all questions in the spaces provided. You have 90 minutes. You must show all work for full credit. There are 6 pages in this exam, and there is also a separate equation sheet. Graphing calculators and calculators that allow alphanumeric input are not allowed. There are 5 questions; the points for each are indicated below. 1. _____________/20 2. _____________/16 3. _____________/16 4. _____________/24 5. _____________/24 Total _____________/100
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of 6 Page 2 of 6 1) (20 points) A thermally insulated vessel contains 1.00 L of water at 10.0°C. Steam (at 110°C, and 1 atm constant pressure) is introduced into this water by means of an open-ended pipe that ends below the surface of the water. The steam condenses and the resulting additional liquid water mixes with the water that is already in the vessel. What mass of steam must be added to the water in the vessel for the final temperature of the total mass of water to be 55°C ? (NOTE, assume that there is no loss of heat from the vessel to the surroundings. You may assume that the specific heat of steam is 1.90 J/g.°C and that of water is 4.18 J/g.°C throughout the temperature range of interest. For the purposes of this question, assume that the standard enthalpy of vaporization of water is 44.0 kJ/mole and is temperature independent. You can ignore the heat capacity of the vessel itself). The amount of heat that is needed to raise the temperature of 1000 g of water from 10°C to 55°C is: (1000 g)(4.18 J/g.°C)(45°C) = 188,100 J, or 188.1 kJ This amount of heat is going to be supplied by X g of steam, originally at 110°C.
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This note was uploaded on 11/14/2009 for the course CHEM 207 at Cornell.

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Chem2080_2009_Prelim1_key - Page 1 of 6 Chemistry 2080 -...

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