What are the applications of the reversible process

Reversible process

A reversible process is a thermodynamic change of state of bodies, which could happen the other way around at any time without the bodies or their surroundings undergoing permanent changes.

Real irreversible Processes with energy dissipation (e.g. friction) produce entropy production inside the system. The following then applies: $ \ Delta S> 0 $. The entropy generation rate, also called the entropy production rate, is always positive.

With ideals reversible Processes no entropy is generated. The entropy production rate is consequently zero: $ \ Delta S = 0 $

Whether a process is reversible or irreversible is defined by the entropy flow generated in the system and not on the change in entropy in the overall system, which depends on entropy flows across the system boundary in the form of heat or material flows. (Compare this with the 2nd law of thermodynamics).[1]

In classical mechanics are all Processes are reversible, in thermodynamics there are changes of state Not reversible or irreversible if they move towards a state of equilibrium in which there are no longer any temperature or pressure differences and from which they can no longer move due to a lack of potential differences. This is mostly the case in reality.

The 2nd law of thermodynamics states that the maximum possible work of the system can only be performed by a reversible process through heat supplied or removed.

In reversible processes, the change $ dS _ {\ mathrm {rev}} $ of the entropy appliesS.:

$ dS _ {\ mathrm {rev}} = \ frac {\ delta Q _ {\ mathrm {rev}}} {T} $

It is

  • $ \ delta Q _ {\ mathrm {rev}} $ the amount of heat converted
  • T the absolute temperature at which the process takes place.

From this it can be concluded for reversible cycle processes (e.g. for the ideal Carnot process) that there is no change in entropy:

$ \ Rightarrow \ Delta S = \ oint \ frac {\ delta Q _ {\ mathrm {rev}}} {T} = 0 $

On the other hand, the following applies to the change in entropy of the system of irreversible processes:

$ dS _ {\ mathrm {irrev}}> dS _ {\ mathrm {rev}} $

Examples of irreversible changes of state are

  • the heat conduction at finite temperature differences
  • the mixing of gases or liquids (compensation of partial pressure differences)
  • Throttling (converting pressure into motion)
  • Friction (conversion of movement into heat).


  • Horst Stocker: Physics paperback. 4th edition, Verlag Harry Deutsch, Frankfurt am Main 2000, ISBN 3-8171-1628-4.
  • Wolfgang Nolting: Basic course Theoretical Physics 4. Special Theory of Relativity and Thermodynamics 6th edition, Springer-Verlag, Berlin 2005, ISBN 3-540-24119-1

Individual evidence

  1. ↑ cf. Weigand, Bernhard: Thermodynamics compact, Heidelberg 2013, p.28ff