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Unformatted text preview: Chapter N  Problems Blinn College  Physics 2425  Terry Honan Problem N.1 What is the change in entropy of 3 kg of water initially at 20 C when it is cooled and frozen resulting in ice at 0C? Solution to N.1 This is a two step problem. D S 1 is the change in entropy when the water is brought from 20 C to 0 C and D S 2 is the change when the water at 0 C freezes to 0 C. When water freezes to ice heat is removed so Q = m L f . The sign of the entropy of the water to water case follows from the values of the temperatures. The temperature must be in Kelvin in all cases here. D S =D S 1 +D S 2 = m c ln T f T i + Q T = m c water ln T f T i + m L f T = 3 4186 ln 273 293 + 3 3.33 10 5 273 = 887.9 3659.3 = 4550 J K Problem N.2 What is the total change in entropy when 3000 J of heat flows into a house at 20 C from the warm exterior at 40 C? Solution to N.2 The entropy of the exterior decreases, since heat flows out of it, and the entropy of the interior increases since heat flows into it.The entropy of the exterior decreases, since heat flows out of it, and the entropy of the interior increases since heat flows into it....
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This document was uploaded on 02/01/2010.
 Spring '09
 Entropy

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