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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What ds>dQ/T mean?

I read the derivation on page 216 over here: https://www3.nd.edu/~powers/ame.20231/notes.pdf First it considers an irreversible process between state 1 and 2 followed by a reversible process between ...
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Increase in entropy principle

If we consider a system to undergo an irreversible process from state 1 to state 2 and a reversible process from state 2 to state 1, then through Clausius inequality $\int_{1}^{2} \frac{\delta ...
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T-Symmetry and spatial symmetry of a multivariate conserved quantity

Definition: A reversible system is defined to be any second-order system that is invariant under the map. $t \mapsto -t$ $y \mapsto -y$ Suppose there exists a multivariate function ...
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Why is heat transfer reversible when temperature difference is infinitesimal?

I don't understand why heat transfer from hot reservoir to the system is considered reversible in this case: $T_{reservoir}$ = $T_{system}$ + dT but it's considered irreversible in this case: ...
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36 views

Question about reversible heat engine efficiency

I have a question regarding heat engines that cropped up whilst I was doing a practice question. I will summarise the results I obtained for the previous parts of the question so as to save your time. ...
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1answer
49 views

Reversible process, equivalence of two definitions?

There are two common definitions of a reversible process: A reversible processes is quasistatic with no dissipation. And A process where an infinitesimal change in conditions would reverse ...
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What Feynman meant in description of reversible machine and levers

In chapter four of the part one of the lectures, he mentions: (..) A machine that we actually use can be, in a sense, almost reversible: that is, if it will lift the weight of three by lowering ...
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132 views

Melting ice: reversible or irreversible?

I am looking into whether the melting of ice (or any substance for that matter) at constant pressure and temperature is reversible or irreversible. Different sources say different things, and it may ...
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1answer
48 views

Entropy generation during irreversible adiabatic expansion

During irreversible adiabatic expansion entropy is generated. It means that the gas expands to as greater volume than that during reversible adiabatic expansion for the same change in pressure. How ...
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1answer
58 views

Why is entropy of system same for reversible and irreversible processes? [closed]

I read that entropy change of universe is zero in a reversible process but positive in a irreversible process,then doesn't it mean that entropy change of system of both the processes must be ...
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60 views

How to conceptually identify reversible and irreversible processes?

When I studied thermodynamics for the first time I didn't really get much the conceptual understanding on reversibility, but nonetheless I've got a rough understanding and a mathematical criterion for ...
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42 views

Questions regarding reversible processes, entanglement, and time reversal symmetry [closed]

Can we, a priori, state that a physical state is entangled with its environment? Its hard for me to come up with a reason for why we can't. For my next question, consider a physical state: ...
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Free expansion of ideal gas, transient phase (3 questions)

We all know the classic scenario of free expansion. A contained gas expands into a vaccum and in the end we have $\Delta T = \Delta U = \Delta H = 0$ and $\Delta S = R \ln \frac{V_2}{V_1}$. This is ...
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47 views

Difference between throtling and adiabatic expansion

Throttling process is an isoenthalpic process.$$U+PV=constant.$$ during throttling process does the gas do work at the cost of internal energy such that its temperature decreases? Then what is the ...
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57 views

Reversibility and isothermal processes

I would like to know why any reversible process has to be isothermal, according to my sources. Why can´t we consider adiabatic processes to be reversible? EDITED ...
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1answer
56 views

reversible vs irreversible work for adiabatic process

I have a gas transitioning adiabatically between A ($P_1$, $V_1$) and B ($P_2$, $V_2$) where $P_1>P_2$ and $V_2>V_1$. The question is to determine the net work done on the gas if the gas is ...
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137 views

Reversible and Irreversible Process

I would like to ask a specific conceptual question which bothers me for quite some time! First of all i do know the difference in between reversible and irreversible processes. What is thought in ...
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1answer
27 views

Entropy change in a calorimetry problem

A standard textbook problem has us calculate the change in entropy in a system that undergoes some sort of heat exchange. For example, object $A$ has specific heat $c_a$ and initial temperature $T_A$ ...
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1answer
81 views

Does time symmetry still holds when a particle drops into a black hole?

When a particle drops into Earth, it hits the ground and rebounds, if time reverse, it is equivalent to another particle moves with same speed but opposite direction. But at the case that a particle ...
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92 views

Heat loss by gas compression - reversible vs. irreversible

I just solved a problem involving the following scenario: A gas following the van der Waals equation of state (not an ideal gas) is placed in a cylinder and undergoes isothermal compression. The ...
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1answer
74 views

“Irreversibility” of the RG flow

In his remarkable work, Zamolodchikov proved a theorem regarding two dimensional QFT Renormalization Group (RG) flow, describing a monotonically decreasing function in the flow parameter which is ...
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186 views

How to calculate quantum cost of a reversible logic circuit?

I am trying to develop new reversible logic synthesis algorithm. But I need a good quantum cost measure for a synthesized circuit to compare my results with existing ones. For now I'm using RCViewer+ ...
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68 views

Thermodynamics and Newton's second law

Is it correct to say, that the Newton's laws (or a Newtonian system) is reversible if the friction isn't considered (the fact that the time is of second order $\frac{d^2x}{dt^2}$) and an isolated ...
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47 views

Reversible expansion paradox

consider a mole of an ideal gas enclosed in a container with a mass-less piston undergoing isothermal reversible expansion. now we know that in an reversible process the system and the environment ...
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Mathematical definition of reversible processes

If I label an initial thermodynamic state as $\psi$ and the final thermodynamic state as $\xi$ then can I say that under a reversible process the two states are related to each other by a continuous ...
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63 views

Dissipative forces and reversible processes

A book that I have contains the following lines: For a process to be reversible, the dissipative forces such as viscosity and friction should be absent. My question is why?
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96 views

A mass falls to the ground from a height. What's the change of the entropy of the universe?

A mass $m$ falls to the ground from a height $h$. The temperature $T$ is constant. What's the change of the entropy of the universe? It's an example in Carter's Classical and Statistical ...
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57 views

How to interpret irreversibility in time?

I'll quote Feynman's Lectures, chapter 52 (Symmetry in Physical Laws) of volume 1: [...] If we see the egg splattering on the sidewalk and the shell cracking open, and so on, then we will surely ...
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What is the physical implication of Clausius inequality?

Clausius inequality is given as: $$\oint \frac{\delta Q_\text{res}}{T_\text{res}} \le 0\;.$$ From Carnot cycle, we get the equality relation as the entropy lost by the hot reservoir is the same as ...
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391 views

Why does slow compression of a gas doesn't change its entropy to increase?

This is quoted from Daniel V Schroeder's Thermal Physics: It's interesting to think about why the slow compression of a gas doesn't change its entropy to increase. One way to think about it is to ...
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1answer
56 views

A question about thermodynamic reversible process [closed]

I am a new learner of thermodynamics, and I have a question in my assignment: Show that $W$ and $Q$ for an arbitraty mechanically reversible nonflow process are given by: $$W=\int VdP - ...
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1answer
60 views

How is one process reversible and its reverse non-reversible?

My textbook gives this example of a reversible process: A gas in a piston is expanded over a long period of time, sitting on a hot plate that maintains its temperature. As an infinitesimal amount of ...
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64 views

Reversible adiabatic process

I was studying some basic thermodynamics concepts and I noticed that in reversible processes in my book always the adiabatic word is used. So are all reversible processes adiabatic? (ques 1) Or ...
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288 views

What experiment supports the axiom that quantum operations are reversible?

Among the axioms of quantum mechanics there is one axiom that says transformations of a quantum state need to be continuous, linear, and reversible (and this together with the other axioms results in ...
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100 views

Is lost work always positive? How to approve?

I am dealing with a question asking for comment on the sign of lost work. The case is to consider an irreversible process and a reversible process which share the same starting and ending state. Is ...
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94 views

How to prove mathematically that the work done during irreversible process is least due to viscosity stress?

This is a known fact that the work done by the system is maximum during reversible processes & least during irreversible processes owing to the viscosity stresses. But can we prove it ...
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Must irreversible heat transfer be quasistatic?

Suppose there is an isolated system composed of two subsystems $A$ and $B$ in thermal contact with each other, but mechanically and diffusively insulated from each other. The system starts off with a ...
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1answer
618 views

Calculation of entropy change in irreversible cycles, meaning of $\delta Q/T$ in irreversible processes

Let's take the two cycles in the pictures working with an ideal gas. We perform one, and then perform the other. The cycle is made reversible by making the gas exchange heat with a heat bath having ...
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2answers
86 views

Difference between a reversible change and a reversible process?

Question In thermodynamics what is the difference between a reversible change and a reversible process? Additional information I am new to the topic of thermodynamics and getting confused about ...
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1answer
134 views

What is reversible and irreversible process? Can process below even be irreversible?

I heard the definitions, but I have much trouble understanding them. My teacher told me that in an example with two chambers and gas particles (look below) entropy increases, but I cannot understand ...
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322 views

If entropy is a state function, then why is all the talk about reversible vs. irreversible processes?

So I'm preparing for my Thermodynamics undergrad exam, and I just can't wrap my head around the significance of reversibility vs. irreversibility of a process in relation to entropy. I mean if entropy ...
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1answer
86 views

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: ...
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Definition of an irreversible process

I'm a little bit confused as to why quasi-static process cannot lose energy to friction in order to be reversible. This is how I'm thinking: Suppose you have a container of gas with a piston, and on ...
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91 views

How can a reversible adiabatic expansion not increase entropy?

In the second stage of the Carnot cycle, a gas is thermally insulated and allowed to expand and do work on the piston. I understand the reason people give is that because entropy is $\,dS = \,dQ/T$ ...
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Generalized Onsager Relation

The usual Onsager reciprocity relations states the first order kinetic coefficients form a symmetric matrix. Are there any such relations (from time reversal symmetry) for higher order kinetic ...
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2k views

Internal reversibility

The concept of reversibility always gives me a hard time.In a reversible process the change of entropy is zero. On the other hand for irreversible process it is not.But there comes another topic which ...
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What happens to magnetic $B$-field in a superconductor in the Bean model?

In the Bean model, as we start applying a magnetic field $H$ in the plane of a slab, the $B$-field inside the superconductor decreases linearly from each side, and at a sufficiently high field $H^{*}$ ...
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CP violation and arrow of time

Does CP (and thus T) violation imply a definite arrow of time? How does it relate to the thermodynamic one? Does the microscopic irreversibility reflect itself to macroscopic level? If not why?
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What are the state variables like temperature after the system has done an adiabatic irreversible process? [closed]

Consider a system containing ideal gas which is initially at a volume $V_{1}$ and then suddenly its volume is increased to a volume $V_{2}$. What is the final temperature of the system if the initial ...
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1answer
68 views

Apparent Contradiction in Helmholtz Free Energy

I am looking at some mathematics of HelmHoltz free energy. Naturally, wikipedia is one of the (hopefully) more reliable sources of information. In its derivation section, the last equation states that ...