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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Why is the final temperature of irreversible adiabatic processes higher than that of reversible adiabatic processes?

Suppose an irreversible adiabatic expansion process and a reversible adiabatic expansion process are starting from the same initial state, say, P1V1. Now, let both of these processes have equal ...
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Are there any time irreversible processes on earth which aren't due to the sun?

The sun is very hot. The earth is cold. Energy always flows from hot to cold systems. Due to the temperature difference, useful energy can be imparted onto earth (i.e., blackbody radiation from the ...
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How do I prove reversible transformations are necessarily quasistatic without using entropy?

I have the following definitions: A transformation is said to be quasistatic if it passes only through equilibrium states (that is, the thermodynamical coordinates of the system are defined at every ...
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How can we say that work done by carnot engine in a cycle equals net heat released into it even when it is operated b/w 2 bodies and not 2 reservoir?

When a carnot engine is operated between 2 reservoir then after each cycle it return to its initial state so change in internal energy is zero and so work done by it equals net heat released into it. ...
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How does a reversible Carnot cycle transform heat to work?

To make clearer what I am asking let me introduce a new terminology to avoid any misunderstandings. Let the heat flow, which is rate, between a reservoir and an engine be denoted by $\mathfrak J$ and ...
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Is it possible for the universe to return to the exact current state if information cannot be lost?

My understanding is that, if information in the universe cannot be lost, it will always be possible (in principle) to tell which prior state of the universe has led to the current state. Is this true ...
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Is determinism broken in special relativity?

Under classical mechanics, in an isolated system everything is deterministic given some initial conditions. Otherwise, we would have to consider some probabilities of interactions with the outside on ...
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Understanding page 141 of Blundell’s Concepts in thermal physics

On this page (in the second edition), there is a figure containing two states A and B of a system: There are two paths between A and B: one is an irreversible change, and the other is a reversible ...
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Why isn't the free expansion of a gas in an adiabatic container isentropic?

If you expand a gas adiabatically using a piston, the process is isentropic. However, if you simply remove the piston and let the gas expand freely, the process is now not isentropic. What makes these ...
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Proof of Caratheodory's theorem

Caratheodory's formulation of second law of thermodynamics, also referred to as Caratheodory's principle states In any neighbourhood of any thermodynamic state $P$ there exist states which are ...
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Understanding the use of $d$ and $\partial$ in thermodynamics

It seems a hundred variations of this question have been asked, and it's difficult to find which of those questions relates to exactly what I'm asking. My apologies if exactly this question has ...
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Defining reversibility without resorting to entropy

Is it possible to define the concept of reversible process without using any mention to entropy? The Wikipedia definition of reversible process seems to accomplish this by stating that: In ...
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Fundaments of thermodynamics and separating entropy

I tried to write down my "own" fundamental rules of thermodynamics, which I can then use as solid ground to understand the rest of the topic. The main thing I thought of is separating ...
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Questions about Maxwell's demon

I've been reading about Maxwell's demon and the current accepted solution for it (deleting information results in an increase in entropy), but there are two things I don't understand about the ...
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What are the requirements to apply the Laplace Law in Thermodynamics ? Reversible and adiabatic, or just adiabatic?

The Laplace's Law in thermodynamics states that an adabatic reversible transformation of a perfect gas verifies the following identity : $$ PV^{\gamma} = cte \qquad \left( \gamma = \frac{C_p}{C_v} \...
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Can heat(?) flow from a cold object to hot object?

When we dip a spoon (stainless steel) into ice cream, does it becomes cold or stay the same temperature? If it does, can we say that heat(?) can flow from cold to hot objects? Is this the reason ...
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Do irreversible thermodynamic processes CONSTITUTE time or do they MOVE IN time? [closed]

Time can be associated with irreversibility. A broken egg can't reassemble. Most, if not all, processes are irreversible and this is associated with time going in one direction. Ŕemarkably, living ...
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Entropy of a deterministic reversible system

Suppose a deterministic reversible system evolving from state A of gas located in a small bottle in an otherwise empty room, to state B where the gas is dispersed throughout the room. Why is the ...
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Why is rapid expansion/compression reversible?

I am looking over the Otto Cycle on this MIT website and it says at one point "the processes from 1 to 2 and from 3 to 4 are isentropic" in reference to the expansion and compression of the ...
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Why is rapid expansion/compression considered a reversible/isentropic process?

I am looking over the Otto Cycle on this MIT website and it says at one point "the processes from 1 to 2 and from 3 to 4 are isentropic" in reference to the expansion and compression of the ...
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Why must all reactions be reversible according to thermodynamics?

I am reading the book "Models of Calcium Signalling" by Dupont et al., and on pages 31-32 the statement is made with regard to some previously written chemical reaction equations We have ...
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Comparing the final pressures/volumes/temperatures of a reversible and irreversible adiabatic process

Consider $2$ ideal and identical gases $A$ and $B$ which are at the same initial state of ($P_1$,$V_1$,$T_1$). $A$ is taken through a reversible adiabatic process and $B$ through an irreversible ...
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Are Hamilton's equations reversible?

Say I define a time dependent vector field $\Psi(t):\mathbb{R}^d\to \mathbb{R}^d$ as reversible (also here) if, for $f(x,y)=(x,-y)$, we have: $$ f\circ \Psi \circ f =\Psi(-t)=\Psi^{-1}(t).$$ Just to ...
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Doubt in entropy change of environment in an irreversible isochoric process

I have read the following:- The entropy change of the environment is calculated by $\Delta S_{env}=-\int \frac{dq_{sys}}{T} $ for that process. Unlike for a system, we do not assume a reversible ...
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Does $PV=nRT$ hold for the endpoints of an irreversible process? [closed]

I have read the following:- $PV=nRT$ holds throughout a reversible process $PV=nRT$ does not hold throughout an irreversible process because the ideal gas law is only applicable for gases in ...
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How can the temperature of the surroundings be constant during a reversible thermodynamic process?

I am having trouble reconciling the following statements I have recently learned about thermodynamics: The temperature of the surroundings is taken to be constant (with only infinitesimal changes) ...
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Why aren't all irreversible processes isobaric?

I am slightly confused about graphs of irreversible processes. Firstly, they are difficult to find and whenever I find them the form is something similar to:- I have read about the explanation given ...
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Using quasistatic processes to calculate quantities

This question is inspired by Reif Problem 5.5. Note that it is not a homework problem and, even if it were, my question only loosely relates to it. A vertical cylinder contains $N$ molecules of a ...
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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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