Processes in Which One Intensive Variable is Constant

Here is our generic process path depicting a series of states the system passes through during a process.
When one intensive property remains constant during a process, it is often designated with an iso- prefix.
State 1
State2
This lesson will explain the special simplifications of the First Law of Thermodynamics that are applicable to

and

Isochoric

processes.
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Ch 4, Lesson E, Page 1 - Processes in Which One Intensive Variable is Constant

• In chapter three, we studied process paths and we learned to construct hypothetical process paths to make it easier for us to evaluate changes in state variables like U and H.
• We built our HPP’s from a series of steps in which just one property of the system changed.
• It turns out that these building blocks in which just one state variable changes are used so frequently that they have their own names.
• Most of the names begin with the “ISO” prefix.  ISO has a Greek origin and in this context it indicates something that does not change.
• So, in an iso-baric process, the pressure does not change.
• In an isothermal process, the temperature does not change.
• In an isochoric process, the volume of the system does not change.
• Keep in mind that if the volume remains constant and the system is CLOSED, then the specific volume, Vhat also remains constant.
• The root words “BARIC” and “CHORIC” may be new to you, so you’ll need to memorize them.
• There are a few other “ISO” type processes that will come up in the course, but not many.
• Now, we are going to apply the 1st Law to isobaric and isochoric processes.
• Our goal is to determine values of the state variables based on the nature of each step using the techniques that we learned in Chapter 3.  Then, we, in some cases, we can use the 1st Law to evaluate Q and W.
• Remember, Q &W are important because they help us evaluate the performance of the process.
• Now, on with the show.