ch20-p007

# ch20-p007 - 7. (a) The energy that leaves the aluminum as...

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() ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 0.200 kg 900 J/kg K 100 C 0.0500 kg 4190 J/kg K 20 C 0.200 kg 900 J/kg K 0.0500 kg 4190 J/kg K 57.0 C 330 K. f T ⋅° + ° = ⋅+ = (b) Now temperatures must be given in Kelvins: T ai = 393 K, T wi = 293 K, and T f = 330 K. For the aluminum, dQ = m a c a dT and the change in entropy is ( ) 330 K ln 0.200 kg 900 J/kg K ln 373 K 22.1 J/K. f ai T f aa a a a T ai T dQ dT Sm c m c TT T §· Δ= = = = ¨¸ ©¹ =− ³³ (c) The entropy change for the water is 330K ln (0.0500 kg)(4190 J kg.K)ln 293K 24.9J K. f wi T f ww w w w T wi T dQ dT c m c T = = = =+ (d) The change in the total entropy of the aluminum-water system is Δ S = Δ S a + S w = 22.1 J/K + 24.9 J/K = +2.8 J/K. 7. (a) The energy that leaves the aluminum as heat has magnitude Q = m a c a ( T ai T f ), where m a is the mass of the aluminum, c a is the specific heat of aluminum,
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## This note was uploaded on 06/03/2011 for the course PHY 2049 taught by Professor Any during the Spring '08 term at University of Florida.

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