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Physics Lesson 13.10.2 - Reversible and Irreversible Processes

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Welcome to our Physics lesson on Reversible and Irreversible Processes, this is the second lesson of our suite of physics lessons covering the topic of Entropy and the Second Law of Thermodynamics, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.

Reversible and Irreversible Processes

By definition, a reversible process is a thermodynamic process that can reverse without leaving any trace in the surroundings. A process can be either reversible or irreversible, i.e. a process that is not reversible, is irreversible.

All examples taken in the previous paragraph are irreversible processes as it is impossible to turn back naturally into the original state the components of the process. Some other examples of irreversible processes include the effects of friction (teeth of a saw cannot seem anymore as new after months of consumption), chemical reactions, expansion of gas in vacuum, etc.

The term "irreversible" does not mean the system cannot turn again to the original state. For example, if you slide a ball along a horizontal surface, it eventually stops due to friction. You can make the ball slide again at the initial velocity but this needs the involvement of an external factor (the human energy) which causes a permanent change in the surroundings (a human needs to consume fresh food to replace the energy lost). Thus, the ball returns to the original state but the environment not.

If the above process were reversible, it would mean the heat energy exchanged due to friction is sent back to the ball. Obviously, this is impossible. Hence, a reversible process is more an idealization than a reality. However, we use the concept of reversible process as a model to explain more realistic processes, similarly to ideal gas model, which is used to explain the behaviour of real gases.

Slow expansion of compression of gases by supplying or taking of heat in small amounts can be considered as an action that produces reversible processes. We can also obtain slow compression by adding small weights on the piston.

You have reached the end of Physics lesson 13.10.2 Reversible and Irreversible Processes. There are 6 lessons in this physics tutorial covering Entropy and the Second Law of Thermodynamics, you can access all the lessons from this tutorial below.

More Entropy and the Second Law of Thermodynamics Lessons and Learning Resources

Thermodynamics Learning Material
Tutorial IDPhysics Tutorial TitleTutorialVideo
Tutorial
Revision
Notes
Revision
Questions
13.10Entropy and the Second Law of Thermodynamics
Lesson IDPhysics Lesson TitleLessonVideo
Lesson
13.10.1Does the First Law of Thermodynamics Explain Everything about Thermal Processes?
13.10.2Reversible and Irreversible Processes
13.10.3The Meaning of Entropy
13.10.4The Second Law of Thermodynamics
13.10.5Heat Engines
13.10.6Carnot Engine

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