EML3100 Thermo - Summer 2001 - Web Lesson

Entropy changes in solids liquids and ideal gases - PAGE 4

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The solution for ideal gases is not as simple as that for solids and liquids because

For IDEAL GASES we can say that


and dividing through by T gives us

Before in our treatment of internal energy for ideal gases, we determined that


and the ideal gas equation gives us
.

Substituting for du and p/T, we get,


and integrating to get the entropy change gives us

The solution to the integral is

which cannot be simplified further since Cvo is a function of temperature.

We will look at how to use this solution later, but for now, we will consider how to use enthalpy to determine entropy changes in ideal gases.
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