# Introduction: Entropy Balances on Closed System

In Chapters 4 and 5, you learned to use mass and energy balance equations to analyze processes and cycles.
Mass and energy balances are based on the fact that in non-nuclear processes, mass and energy are neither created nor destroyed. Mass and energy are conserved.
In this lesson, you will learn to write entropy balance equations for processes that take place in closed systems.
The problem is that entropy is NOT conserved. In all real processes, entropy is created!
Therefore, the key to writing an entropy balance is the concept of entropy generation that we introduced in Lesson 7C.
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### Ch 8, Lesson A, Page 1 - Introduction: Entropy Balances on Closed System

• We have applied mass and energy balances to a wide variety of systems.
• They have helped us solve just about every problem we have encountered since the beginning of chapter 4.
• In this chapter, we will spend a great deal of time developing and using entropy balance equations.
• There is one small problem.  Although mass and energy are conserved, entropy is NOT.
• In fact, in all real processes, entropy is created or generated.
• Therein lies the key. Entropy generation is just one more term in our entropy balance equation.
• In this short lesson, we will develop an entropy balance equation for closed systems.
• In the next lesson, we will develop entropy balance equations for open systems.
• Now that you know where we are going, let’s get moving.