# General Form of the 1st Law for Open Systems

Mass In
Mass In
Mass In
Mass Out
Mass Out
Open
System

## 1st Law: Enthalpy Form, Muliple Inlets & Outlets

We derived this equation in the previous lesson.
In this lesson, we will apply this equation to a variety of important, practical systems.
These systems are the building blocks of all of the important cycles that we will study later in this course.
Each application in this lesson involves different simplifications of the 1st Law, but all of the systems in this lesson have one thing in common: they operate at steady-state.
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### Ch 5, Lesson C, Page 1 - General Form of the 1st Law for Open Systems

• This course builds towards the study of thermodynamic cycles.
• Most of the thermodynamic cycles that we will study are made up of a series of processes that take place in open systems operating at steady-state.
• In this lesson, we will apply the 1st Law to a variety of steady-state processes.
• In all of the later chapters, we will use these processes as building blocks to assemble a wide variety of power, refrigeration and heat pump cycles.
• Each system that we study in this lesson has its own characteristics that allow us to simplify the general form of the 1st Law in different ways.
• But they all have one characteristic in common:  they operate at steady-state.
• But what, exactly, does steady-state mean ?
• That is the topic that we need to address first in this lesson
• Flip the page and let’s get started.