Questions tagged [reversibility]

The potential for a thermodynamic process to be reversed in time. Alternatively, a quantification of how far an irreversible process is from being reversible, which relies on a comparison to a corresponding theoretical reversible process.

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In order to explain a reversible change in thermodynamics, why is the following description irreversible?

I have a book that explains reversible processes as follows: A reversible change in thermodynamics is a change that can be reversed by an infinitesimal modification of a variable. [...] Suppose a gas ...
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Why does a null entropy variation along a closed timelike curve imply a reversible process?

Carlo Rovelli in one of his articles from 2019 (reference: https://arxiv.org/abs/1912.04702) argues that time travel into the past are thermodynamically impossible: For instance, if we want to travel ...
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What is the type of system, if I have an opened container with hot water inside, but no heat input to the system?

I have a school project, where I am trying to generate electricity using TEG modules that are attached to an aluminium container that contains hot water. The container is opened and there is no heat ...
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How to find a complete understanding the 2nd law of Thermodynamics in terms of forms?

I have two straightforward question, and below I introduce more context to interpret them: What is, or is there, an order relation for forms that one can use to make sense of the 2nd law of ...
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Confusion with Gibb's energy [duplicate]

For a reversible process , I can show that $$\mathrm dG=0$$ For the same reversible process I can also prove that $$\mathrm dG=\mathrm dW_{\text{max, non } P-V\text{ work}}$$ Does that imply maximum ...
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What's the variation of entropy of an irreversible process?

I'm studying entropy, in particular the increase of entropy principle, and I have a doubt about the entropy variation of an irreversible transformation. If I have two thermodynamic states, A and B, ...
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Quantum and classical physics are reversible, yet quantum gates have to be reversible, whereas classical gates need not. Why?

I've read in many books and articles that because Schrödinger's equation is reversible, quantum gates have to be reversible. OK. But, classical physics is reversible, yet classical gates in classical ...
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How is entropy a state variable, and how can we measure entropy from irreversible processes with reversible ones, from a Khan Academy video

My questions : How is entropy a state variable? Why can we use a reversible process to measure an irreversible process's change in entropy if irreversible processes generate extra (unaccounted for ...
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Why is $TΔS$ a good approximation for calculating heat transfer during heating/cooling in real life?

So various books and sources have agreed on defining specific heat capacity (formally) to be: $$c_v=\frac{T}{n}\left(\frac{\partial S}{\partial T}\right)_V=\frac{1}{n}\left(\frac{\delta Q_{reversible}}...
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Entropy variation due to heat transfer [duplicate]

There is a system at temperature $T_1$ in thermal contact with the environment which temperature is $T_2>T_1$. The entropy change of the system, due to heat transfer, has been calculated as: $$dS_1=...
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How can a quasi-static process be reversible?

As I understand it, a reversible process is required to be quasi-static because each infinitesimal step in a quasi-static process generates only infinitesimal amounts of entropy at a time which can be ...
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Time's Arrow and QM

Something puzzles me. It is sometimes said that the fundamental equations of physics are time-reversible, creating the problem of time's arrow. But... isn't Schrodinger's wave equation time-dependent? ...
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Doubt in the spontaneous process definition

Using the following definition I don't understand why a reversible process is not spontaneous. For an isolated system, a reversible process happen without any outside intervention. reversible process: ...
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In the Langevin dynamics: neglecting inertia. A mathematician trying to understand physics terminology

If we write the Langevin equation: for a particle with mass $m$, position $x$ and velocity $v$, with some damping coefficient $\gamma$, $$ m dV(t)=-\gamma V(t)dt+dW(t) ,~~~~~~~dX(t)=V(t)dt.$$ Then as $...
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How do we physically reverse a classical wavepacket?

Imagine a classical dispersive Gaussian wavepacket (GW). In a wonderful answer by @Qmechanic, to this question (who seems to do much tagging these days, with an occasional well-aimed-and-hit answer), ...
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Confused about Reversible and Irreversible processes

Let us look at this situation. Consider a container having a gas trapped inside, facing pressure from masses M1 and M2, assume that this system is at equilibrium. Here point A represents the initial ...
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Why is the Joule-Thomson-process irreversible?

It is always said that the Joule-Thomson process is irreversible, but why? Reversible means that the process is invertible, i.e. if the external conditions are reversed, the process itself is reversed....
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Is net entropy change 0 when we slowly increase concentration of a gas in a closed container at thermal contact with the environment?

I suspect that the answer for the following question is no, but I hope I am wrong. Consider the following process. An ideal monoatomic gas is in a closed container, which is in thermal contact with ...
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Ill-posed problem about themodynamic work? (comparing reversible and irreversible for different final states)

I'm not concerned with the answer itself or the points for this assignment. My interest is in whether this problem is ill-posed, or can in fact be solved with the given information. I am under the ...
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Is Callen really being sloppy saying $\text{đ}Q=T\mathrm{d}S$ for *all* quasi-static processes?

I am reading Callen's Thermodynamics and introduction to Thermostatics (second edition). The textbook says in chapter 4-2 that $\text{đ}Q=T\mathrm{d}S$ always holds for quasi-static processes, ...
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Understanding Callen's eq. (4.9) and the maximum work theorem

I'm currently reading Herbert B. Callen's Thermodynamics and an Introduction to Thermostatics, II ed, and I don't quite understand the last few propositions made on page 105 (a scan attached below). ...
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Derivation of 1st law of thermodynamics using microcanonical ensemble

In the book Statistical Physics of Particles by M. Kardar, the author shows the connection between the microcanonical ensemble and thermodynamics deriving the zeroth, 1st and 2nd laws. In the ...
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The Work Done by an Irreversible Carnot Cycle

This is a question from the book, Understanding Non-Equilibrium Thermodynamics by Lebon and Jou. Show that the work performed by an engine during an irreversible cycle operating between two thermal ...
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Uniqueness of Irreversible and adiabatic processes in finite time

Let the external intensive and extensive "mechanical" variables be denoted by $Y_k, X_k$. These variables are well defined irrespective of the system is in equilibrium or not. For an ...
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Can adiabatic heat exchange between different temperatures ever be reversible?

I've been told, A volume 2X of Temperature 0.5*(T1+T2) is always at higher entropy than thermally insulated volumes, 'X' at T1, 'X' at T2 put together. Let's take Sys1 (A volume 2X of Temperature 0.5*(...
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Area under $T$-$s$ diagram for an internally reversible process? [closed]

In Cengel and Boles, it is said that the area under a $T$-$s$ diagram for an internally reversible process is equal to the total heat transfer during the process. The example given of an internally ...
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Unitary Time Evolution and Reversibility

I have a system as follows: $$\frac{d\mathbf{x}}{dt} = -iA \mathbf{x},$$ which describes the time evolution of variables $\mathbf{x}$ according to the matrix $A$. Now, $A$ is not Hermitian, but has ...
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Thermodynamic calculations for irreversible processes

In Q5.5 of Sethna 'Entropy, Order, Parameters and Complexity', we are presented with a pressure-volume diagram for a process on a monoatomic ideal gas consisting of the following steps: "(a) ...
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Why the irreversible work carried in an adiabatic condition never causes change in internal energy?

I saw the lecture of thermodynamics on the MIT opencourse ware . In that lecture , the professor said that change in internal energy in an adiabtic process is caused by only reversible work , and not ...
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How does entropy stay constant for an isobaric process?

What I understand (Isothermal process): In an isothermal process, the net entropy stays constant. Suppose, I have a cylinder filled with a monoatomic ideal gas. Now, I place it on an infinitely large ...
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Entropy in a reversible process

According to 2nd law of thermodynamics entropy never decreases, it's either zero or bigger. The problem with the definition is that it doesn't specify WHICH entropy never decreases? Of the system that ...
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What does the concept of "Entropy Flow" mean in detail?

Recently a found a paper on the thermoelectric effect: https://williamsgj.people.cofc.edu/Thermoelectric%20Effect.pdf When I started with Chapter 5 "Irreversible Thermodynamics" I struggle ...
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Reversibility of the arrow of time

I often read in physics vulgarisation books about how paradoxal it is that the time seems to go only one direction, as entropy grows with time, and nobody has ever seen a broken cup repair itself and ...
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Is gravitational redshift reversible?

Imagine a scenario where a LASER beam is shot from the surface of one planet to a detector on another. Assume there are no atmosphere and nothing affects the beam in any way between the planets. ...
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Reversible process and reversible cycle

Is there a difference between the two when it comes to how entropy behaves? I am thoroughly confused regarding reversible process for a system, irreversible process, rev cycle, irreversible cycle, ...
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Why do seemingly asymmetric processes in nature have a non-zero probability to occur backwards?

Only certain types of processes (energy transfer and transformation) actually take place in nature, which is governed by the second law of thermodynamics, and the unidirectional nature of these ...
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Entropy and reversible and irreversible processes

If we have a system that goes from equilibrium state A to B, since entropy is a state function then for the entropy change we would have: $\Delta S = S_B - S_A$ Since entropy is a state function it is ...
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Entropy description as in statistical mechanics but of transition phase between equilibrium states

In statistical mechanics, entropy is defined based on possible number microstates. However, the entropy is defined only for equilibrium cases. For example, when two bodies of different temperature are ...
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Derivation of reversible flow work for open systems

In derivation of steady reversible flow work, what sort of model are we considering, when we write the differential form of first law as $$\delta w=\delta q- dh-vdv - gdz $$ for one inflow and one ...
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What makes procesess internally reversible? [closed]

So I read that processes where there is no thermal gradients in the system are internally reversible, but for other cases, do we have to consider the temperature of boundary to calculate entropy ...
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Is this set up a reversible process and is the adiabatic equation of state applicable here?

I had this question in a recent test: My teacher while discussing this question used the adiabatic equation of state PV^gamma=constant to solve for length L (options C and D). And used work energy ...
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Approximation of any reversible process by carnot cycle

While studying thermodynamics i came across the fact that any reversible cycle can be represented by series of miniature carnot cycles. I am unable to understand how can it be done for every cycle as ...
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Is falling in vacuum reversible or irreversible process?

Process is reversible if you can return to initial state through the same intermediate equillibrium states and cause infinitesimaly small changes in surrounding area. Does that mean that falling in ...
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Clausius inequality leading to absurd result

Background: After deriving Clausius inequality, the author of this book derives the following relation: Consider the cycle shown in the figure in which leg $A \rightarrow B$ is irreversible. In the ...
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Why do reversible processes have to be quasi-static?

I have already read two posts on this topic (here and here) and was still confused on what it is about a quasi-static process that makes it reversible. The answer that has gotten me closest to ...
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How does coarse-graining lead to irreversibility?

This is how I used to understand how coarse-graining leads to irreversibility. Suppose that we start with a coarse-grained phase space and two initial conditions belonging to two different phase cells....
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Past prediction of a damped harmonic oscillator (a follow-up of a previous question)

Consider an ordinary differential equation (ODE) of a 1D damped oscillator of the form $$\ddot{x}+\gamma\dot{x}+\omega^2x=0.~~(\omega^2,\gamma>0)$$ I want to know if this ODE is reversible i.e., ...
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How can entropy increase on irreversible paths in an isolated system?

I seem to be able to contradict the second law of thermodynamics. What am I missing? $dS = \frac{\delta q}{T}$ along reversible paths $S$ is a potential: $\Delta S_{A \to B} = \int_\gamma\frac{\delta ...
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Does an irreversible thermodynamic process always increase the entropy?

I know that if over the a given thermodynamic process the entropy of the universe increases, then that process is irreversible. But does the opposite also hold true, i.e. do all irreversible processes ...
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Relation between reversible and irreversible nature of engine and its entropy [closed]

please someone tell me about the relationship of the reversible and irreversible nature of an engine and how is it related to its change in entropy
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