Thermodynamic Processes: Isobaric, Isochoric, Isothermal & Adiabatic Video

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  • 0:02 What are the…
  • 1:50 Isobaric Process
  • 2:32 Isochoric Process
  • 2:55 Isothermal Process
  • 4:01 Adiabatic Process
  • 4:47 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

Learn about the four thermodynamic processes and how they work: isobaric, isochoric, isothermal and adiabatic. See if you can tell the difference by taking a quiz.

What Are Thermodynamic Processes?

Everyone is hot. Or rather, everyone has heat. Every atom and molecule in your body undergoes constant random motions that are impossible to predict. Those random motions are what we call heat energy.

Thermodynamics is the study of the movement of heat. If you touch a block of ice, it isn't always pleasant unless it's a really hot day. If you touch a hot pan out of the oven you'll burn yourself. Both of those things happen because of how fast heat is moving. The heat from the hot pan moves into your hand rapidly, and when touching an ice cube, you lose your own body heat fast. Heat transfers from hot places to cold places - or in other words, heat spreads out. Extreme heat or cold can damage our tissues, so it's a pretty important thing to understand. It's also how we've been able to build refrigerators and large insulated coolers to take to the beach.

These are examples of the many things we can do with heat if we understand how it moves within or between systems. A system is just a particular object or area we're looking at. Our system could be the inside of a thermos flask, or it could be the whole human body or just our skin, or the gas inside a piston. We choose the system we want to look at for convenience.

Then we can look at how heat moves in, out and within that system. We can look at how the system changes. A thermodynamic process is any process that involves heat energy moving within a system or between systems. In this lesson, we're going to look at the four types of thermodynamic processes.

The Four Types of Thermodynamic Processes

The four types of thermodynamic process are isobaric, isochoric, isothermal and adiabatic. Those terms are pretty hard to understand just from the names, so let's break them down one at a time.

Isobaric Process

An isobaric process is one where the pressure of the system (often a gas) stays constant. 'Iso' means the same, and 'baric' means pressure. Pressure is related to the amount of force that the molecules apply to the walls of the container. Imagine that you have a gas inside a movable piston and you heat that gas up. By heating the gas up you make the molecules move faster, which would normally increase the pressure. But at the same time the piston expands, increasing the volume and giving the molecules more room to move. Since the walls of the container are now bigger, the pressure can stay the same even though the molecules are moving faster. That makes it an isobaric process.

Isochoric Process

An isochoric process is one where the volume of the system stays constant. Again, 'iso' means the same and 'choric' means volume. Volume is the amount of space the material takes up. So this would be like heating a gas in a solid, non-expandable container. The molecules would move faster and the pressure would increase, but the size of the container stays the same.

Isothermal Process

An isothermal process is one where the temperature of the system stays constant. Thermal relates to heat, which is in turn related to temperature. Temperature is the average heat (movement) energy of the molecules in a substance.

An example of an isothermal process would be if we took a gas held behind a movable piston and compressed that piston: the volume has decreased, and the pressure behind the piston has increased, since the molecules have less space in which to move. When you compress a piston, you're using energy - you're doing work on the gas - so normally the molecules would gain energy and move faster, and the temperature would increase. So the only way for an isothermal process to happen is if all that energy you put into compressing the gas comes out again, for example by putting a cold reservoir in contact with the piston.

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