# 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

#### or

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

. Entropy will enable us to apply the

#### 2nd Law

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

#### entropy

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

#### entropy

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

• In chapter 6, we used the 2nd Law to analyze thermodynamic cycles.
• Our goal in this chapter is to develop a way to use the 2nd Law to analyze the individual processes that make up a thermodynamic cycle.
• This will let us quantitatively evaluate a real process by comparing its performance to the performance of an ideal reversible process.
• In this lesson we pick up where we left off in the previous lesson.  At the end of lesson A, we introduced a new property or state variable.
• We call that new property entropy.  Entropy is the central concept in this chapter and chapter 8.  The bottom line is that entropy is just as important and useful as internal energy and enthalpy when it comes to the analysis of processes and cycles.
• In this lesson, we will become familiar with some practical aspects of using the new property, entropy.
• We will learn how to find entropy data in the NIST WebBook.
• Finally, we will introduce two new phase diagrams that involve entropy.
• We will learn how these diagrams can give use some insight into the nature and behavior of thermodynamic processes and cycles.
• Now that you know where we are going, let’s get started.