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Unformatted text preview: methane would rise to
116.6 K (a rise of 1.6 K) during the throttling process. 7–9 I THE ENTROPY CHANGE OF IDEAL GASES An expression for the entropy change of an ideal gas can be obtained from
Eq. 7–25 or 7–26 by employing the property relations for ideal gases
(Fig. 7–31). By substituting du Cυ dT and P RT/υ into Eq. 7–25, the differential entropy change of an ideal gas becomes
Pυ = RT
du = Cυ dT
dh = Cp dT ds Cυ dT
T R dυ
υ (7–30) The entropy change for a process is obtained by integrating this relation
between the end states:
FIGURE 7–31
A broadcast from channel IG. 2 s2 s1 1 Cυ(T) dT
T R ln υ2
υ1 (7–31) cen54261_ch07.qxd 11/18/03 9:57 AM Page 297 297
CHAPTER 7 A second relation for the entropy change of an ideal gas is obtained in a
similar manner by substituting dh Cp dT and υ RT/P into Eq. 7–26 and
integrating. The result is
2 s2 s1 1 Cp(T) dT
T R ln P2
P1 (7–32) The specific heats of ideal gases, with the exception of monatomic gases, depend on temperature, and the integrals in Eqs. 7–31 and 7–32 cannot be performed unless t...
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 Spring '09

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