Introduction to Entropy

Before this chapter, we had only used the

2nd Law

to help us analyze

thermodynamic cycles

The overall goal is to find a way to analyze an individual process that will help us evaluate a real process by comparing its performance to the performance of a

reversible process

In the previous lesson, we used the

2nd Law

(in the form of the

2nd Carnot Principle

) for the first time in the analysis of a single process. In this analysis, we discovered a new



state variable that turns out to be every bit as important and useful as internal energy and enthalpy.
In this lesson, we give our new property a name:


. Entropy will enable us to apply the

2nd Law

to processes and to quantitatively assess and compare their performance.
Once we have defined


, we will spend the rest of the lesson learning how to find, use and interpret


data in both tabular form (NIST WebBook) and in graphical form (phase diagrams).
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Ch 7, Lesson B, Page 1 - Introduction to Entropy