P21_060 - 60. (a) The ideal gas is diatomic, so f = 5 (see...

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Unformatted text preview: 60. (a) The ideal gas is diatomic, so f = 5 (see Table 20-3). Since this is an isobaric (constant pressure) process, with no change in the number of moles, then the ideal gas in ratio form (see Sample Problem 20-1) leads to V f V i = T f T i = 8 3 . With C V = f 2 R , Eq. 21-4 gives S gas = nR ln 8 3 + n 5 2 R ln 8 3 where n is the number of moles (25 mol), not to be confused with the number of reservoirs (also denoted n in the later parts of this problem). Consequently, we obtain S gas = 7 2 (25 mol) 8 . 31 J mol K ln 8 3 = 713 J / K . Since Q = nC p T for this process, the entropy change of the reservoir (which transfers energy Q to the gas, so it (the heat) is negative-valued in this context) is (using Eq. 21-2) S res = Q T = n ( 7 2 R ) (800 K 300 K) 800 K = 454 J / K . Therefore, S system = S gas + S res = 259 J/K....
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This note was uploaded on 11/12/2011 for the course PHYS 2001 taught by Professor Sprunger during the Fall '08 term at LSU.

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