What is Irreversible processes: Definition and 19 Discussions

In science, a process that is not reversible is called irreversible. This concept arises frequently in thermodynamics.
In thermodynamics, a change in the thermodynamic state of a system and all of its surroundings cannot be precisely restored to its initial state by infinitesimal changes in some property of the system without expenditure of energy. A system that undergoes an irreversible process may still be capable of returning to its initial state. However, the impossibility occurs in restoring the environment to its own initial conditions. An irreversible process increases the entropy of the universe. Because entropy is a state function, the change in entropy of the system is the same, whether the process is reversible or irreversible. The second law of thermodynamics can be used to determine whether a process is reversible or not.
Intuitively, a process is reversible if there is no dissipation. For example, Joule expansion is irreversible because initially the system is not uniform. Initially, there is part of the system with gas in it, and part of the system with no gas. For dissipation to occur, there needs to be such a non uniformity. This is just the same as if in a system one section of the gas was hot, and the other cold. Then dissipation would occur; the temperature distribution would become uniform with no work being done, and this would be irreversible because you couldn't add or remove heat or change the volume to return the system to its initial state. Thus, if the system is always uniform, then the process is reversible, meaning that you can return the system to its original state by either adding or removing heat, doing work on the system, or letting the system do work. As another example, to approximate the expansion in an internal combustion engine as reversible, we would be assuming that the temperature and pressure uniformly change throughout the volume after the spark. Obviously, this is not true and there is a flame front and sometimes even engine knocking. One of the reasons that Diesel engines are able to attain higher efficiency is that the combustion is much more uniform, so less energy is lost to dissipation and the process is closer to reversible.All complex natural processes are irreversible. The phenomenon of irreversibility results from the fact that if a thermodynamic system, which is any system of sufficient complexity, of interacting molecules is brought from one thermodynamic state to another, the configuration or arrangement of the atoms and molecules in the system will change in a way that is not easily predictable. Some "transformation energy" will be used as the molecules of the "working body" do work on each other when they change from one state to another. During this transformation, there will be some heat energy loss or dissipation due to intermolecular friction and collisions. This energy will not be recoverable if the process is reversed.
Many biological processes that were once thought to be reversible have been found to actually be a pairing of two irreversible processes. Whereas a single enzyme was once believed to catalyze both the forward and reverse chemical changes, research has found that two separate enzymes of similar structure are typically needed to perform what results in a pair of thermodynamically irreversible processes.

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  1. A

    Irreversible isothermal Process Work External pressure not provided

    It is clear that the process is isothermal else it is not possible to find heat absorbed. $$W=-P_{ext}(\Delta V)$$ However ##P_{ext}## is not given. How do I proceed? I tried taking ##W=-(P_2V_2-P_1V_1+P_3V_3-P_2V_2)=\Delta(PV)## but it is wrong for obvious reasons.
  2. V

    B Entropy change for reversible and irreversible processes

    I came across the following statement from the book Physics for Engineering and Science (Schaum's Outline Series). I cannot seem to find a satisfactory answer to the questions. Is the statement in above screenshot talking about entropy change the statement of Second Law of Thermodynamics or is...
  3. hyksos

    A Wave Function Collapse and Thermodynamic Irreversible Processes

    Very early in the development of thermodynamics, it was realized that the 2nd Law of Thermodynamics is not a law fundamental to the fabric of our cosmos, but only becomes true in the limit of the number of particles. It was none other than Boltzmann himself who realized and articulated this...
  4. R

    I The relationship between reversible and irreversible processes

    Hi all. I am referencing the example given in Halliday and Resnick, Chapter 20, Section 1, Subsection "Change in Entropy". The above picture is graph of the free expansion of a gas into a volume that is double its original volume. I n a free expansion there is no heat transfer, the pressure...
  5. P

    Thermodynamics Problem: Reversible and Irreversible Processes

    Attempt at A Solution Problem 1 Reversible Process - A cylinder of ideal gas at pressure P is in mechanical equilibrium with a piston of area A driven by a spring of force F = PA and thermal equilibrium with a reservoir of temperature T. The piston is moved a small distance dx toward the...
  6. cianfa72

    I Adiabatic irreversible process vs adiabatic reversible

    Hi, consider an adiabatic irreversible process carrying a thermodynamic system from initial state A to final state B: this process is accompanied by a positive change in system entropy (call it ##S_g##). Then consider a reversible process between the same initial and final system state. Such...
  7. H

    A Irreversible processes. Heat equation, diffusion equation

    Both the heat equation and the diffusion equation describe processes which are irreversible, because the equations have an odd time derivative. But how can these equations describe the real world when we know that all processes in nature are reversible, information is always conserved? But these...
  8. Decimal

    Work done in reversible and irreversible processes

    Hello, I am encountering some confusion understanding the difference in working with reversible and irreversible processes in thermodynamics. Let's say I have a process where an ideal gas at a certain starting temperature ##T_i## expands from volume ##V_i## to ##V_f##. The temperature of the...
  9. A

    Reversible Work and Irreversibility

    I am trying to grasp the concepts of reversible work, irreversible work and irreversibility.(Last one is the difference between them if i am not mistaken.) Let us consider a rigid and evacuated container at volume V. Then, a valve opens and athmospheric air (P0, T0 is filling the tank. The wall...
  10. kelvin490

    Why dU may not equals dW in free expansion?

    From a video lecture, it is mentioned that "dU≠dW in Joule's free expansion if the process is irreversible and adiabatic" Mentioned in around 36:00-38:00 in the video: What I would like to ask is why in this irreversible adiabatic process, dU≠dW? Is it because the W here doesn't include other...
  11. R

    Entropy change in irreversible processes

    The equation for entropy S=delta(Q)/T is derived from reversible processes such as Carnot cycle. The delta(Q) in the equation is the reversible heat added or taken out from the system. So, why is this equation valid in the case of processes like cooling of a body which is irreversible?
  12. H

    How do we measure gibbs free energy for irreversible processes?

    I know that gibbs free energy for say a body will be equal to = Gibbs free standard energy at 1M and Ph7(-rtlnkeq) (Where k is the concentration of product/ concentration of reactant at equilibrium)+rtlnk. How can we use the standard gibbs free for irreversible spontaneous processes? Is it...
  13. J

    Q) Reversible and Irreversible processes

    I am studying Reif's Fundamental of Statistical and Thermal Physics. (p.91) he explain about Reversible and Irreversible processes by using "The number of accessible states in equilibrium(Ω)". in his point of view, each accessible states have equal probability. comparing to weather...
  14. N

    Change in Entropy for Irreversible Processes

    I was following along in my Thermodynamic textbook and began playing with some definitions. In the following formulation, I somehow managed to prove (obviously incorrectly) that dq = TdS for even irreversible processes. I was hoping someone could point out where in the proof I'm going wrong...
  15. Z

    Entropy for Reversible and Irreversible Processes

    Hello everyone, I've been reviewing some concepts on Thermodynamics and, even though I feel like I am gaining a level of comprehension about the subject that I could not have achieved before as an undergraduate, I am also running into some situations in which some thermodynamic concepts seem to...
  16. O

    First Law of Thermodynamics for Irreversible Processes

    Hello everyone. I have found quite a lot of conflicting information about the first law applied to irreversible processes and in particular whether the dS term in the equation dU = TdS - pdV only accounts for the entropy transferred or for the total entropy, i.e. dS_transferred + dS_created...
  17. R

    Mechanical roots of irreversible processes

    In trying to understand the underlying mechanics of irreversible processes, I came up with four mechanical asymmetries that seemed relevant to describe energy transfer through the bulk motion of a frictionless piston that divides a cylinder with two gasses of same pressure but different...
  18. L

    Thermodynamically irreversible processes

    Hi, I was wondering something. Exactly what is meant by a thermodynamically reversible/irreversible process? What are their relation to spontaneous processes? These concepts seem to be fundamental to the understanding of the second law, but textbooks (including the industry standard Atkins...
  19. A

    Free energy and irreversible processes

    Hi, I'm working on a problem of the thermal stability of a protein. Conventionlly, people compare protein thermal stability in terms of the Gibbs free energy difference between the native and unfolded state. So if it reversibly falls apart, then for N <==> U, DG(N-U) is accessed from the...