hw13solutions - Niu (qn269) HW13 Tsoi (58020) 1 This...

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Unformatted text preview: Niu (qn269) HW13 Tsoi (58020) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Given: specific heat capacity = 4180 J / kg C and latent heat of vaporization of water = 2 . 26 10 6 J / kg . You have 92 g of steam at 100 C. How much heat must be removed to change it to 92 g of water at 15 C? Correct answer: 2 . 40608 10 5 J. Explanation: Given : m = 92 g = 0 . 092 kg , c = 4180 J / kg C , L v = 2 . 26 10 6 J / kg , T o = 100 C , and T f = 15 C . First, the steam must be condensed into water( Q = mL v ), then the water must be cooled( Q = mc T ). Thus the heat loss is Q = mL v + mc T = mL v + mc ( T o- T f ) = (0 . 092 kg) (2 . 26 10 6 J / kg) + (0 . 092 kg) (4180 J / kg C) (100 C- 15 C) = 2 . 40608 10 5 J . 002 10.0 points Given: specific heat of water = 1 cal / g C and latent heat of ice = 79 . 7 cal / g One liter of water at 42 C is used to make iced tea. How much ice at 0 C must be added to lower the temperature of the tea to 20 C? Correct answer: 220 . 662 g. Explanation: Given : m w = 1 L = 1000 g , c w = 1 cal / g C , T h = 42 C , T c = 20 C , T = 0 C , and L ice = 79 . 7 cal / g . Q melt ice + Q raise to 10 C = Q lost by water m ice L ice + m ice c water T ice = m water c water T water m ice = m water c w T w L ice + c w T ice Since L ice + c w T ice = (79 . 7 cal / g) + (1 cal / g C) (20 C- C) = 99 . 7 cal / g then m ice = m water c w ( T h- T c ) L ice + c w ( T c- T ) = (1000 g) (1 cal / g C) (42 C- 20 C) 99 . 7 cal / g = 220 . 662 g . 003 10.0 points When water freezes 1. the temperature of the water decreases. 2. there is no heat exchange with the sur- roundings. 3. heat is absorbed from the surroundings. 4. the temperature of the water increases. 5. heat is given off to the surroundings. cor- rect Explanation: While water freezes, it gives away heat to the surroundings but its temperature remains the same; in addition, its volume increases. 004 (part 1 of 2) 10.0 points Niu (qn269) HW13 Tsoi (58020) 2 A 1 . 1 kg bar of copper is heated at atmo- spheric pressure of 1 . 013 10 5 N / m 2 ....
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This note was uploaded on 09/01/2009 for the course PHY M taught by Professor Staff during the Spring '09 term at University of Texas at Austin.

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hw13solutions - Niu (qn269) HW13 Tsoi (58020) 1 This...

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