# 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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