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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Hysteresis and dissipation

Hysteretic phenomena are often linked to dissipation. When there is an hysteresis loop, the dissipated energy can usually be computed as the area of the cycle. For example, in ferromagnetic materials,...
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1answer
16 views

Why does a soda bottle foam or froth when dropped? [duplicate]

Secondly, if I do drop a soda bottle how long do I have to keep it for it to return to its original state or condition, I.e. safe to open without froth spraying everywhere; or is there some rule of ...
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1answer
55 views

Which temperature does $T$ in Clausius inequality ($\oint \frac{\delta Q}T\le 0$) refer to?

I got a little confused about the temperature in Clausius inequality. As you can see in this answer of Luboš Motl, it seems that temperature is the temperature of the system. But in some answers of ...
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2answers
228 views

Work done in adiabatic reversible process

I was solving a problem on turbine.the steam works on turbine adiabatic reversibly .Is change in enthalpy or is it change in internal energy which equal this work?
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2answers
45 views

Pressure Difference affecting reversibility of a process

It is said that for a finite pressuredifference between system and the surrounding the process is irreversible. From the diagram can you please tell me how the process is irreversible ? Does this ...
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0answers
8 views

Pressure factor affecting reversibility of a process [duplicate]

It is said that for a finite pressure difference between system and the surrounding the process is irreversible. From the diagram can you please tell me how the process is irreversible ? Does this ...
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2answers
758 views

About Boltzmann H-theorem

What is the assumption for Boltzmann H-theorem? One can derive it just from the unitarity of quantum mechanics, so this should be generally true, does it imply a closed system will always thermalize ...
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1answer
39 views

Principle of Maximum Work for Different Paths

The principle of maximum work states that for any process between two states, the work done by the system is maximised for a reversible process (and heat transfer is minimised), and that the work done ...
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1answer
44 views

Prove all reversible heat engines that work between just two temperatures have the same efficiency

Can someone explain this explanation to me: A completely different argument focuses on the requirement that the device only move heat at one or other of the two temperatures. Then, provided ...
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3answers
266 views

Entropy change in an irreversible process between 2 equilibrium state

Calculating entropy change in an irreversible process between 2 states requires computing the change in entropy for any reversible process between the 2 same states, but why? If someone could provide ...
4
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2answers
209 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 ...
7
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5answers
573 views

Definition of entropy in thermodynamics

In most textbooks, the definition of entropy in reversible processes on a system $S$ is given simply as $$d S=\delta Q/T.$$ It seems to me this definition is insufficient since it does not specify ...
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1answer
149 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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5answers
440 views

Change in entropy when mixing water at different temperature

Suppose two amounts of water of the same mass, but with different temperature, are mixed. Then the entropy of the hot water decreases, but the entropy of the cold water increases due to heat transfer. ...
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1answer
46 views

How is a irreversible process (conventionally) represented on a $T-S$ plane and why cannot it be (really) represented?

A reversible process can be represented on a $T-S$ plane, and the area under the curve is the heat exchanged by the system. On $P-V$ plane a irreversible process is conventionally represented with a ...
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3answers
103 views

Is reversible work a point function?

The potential of a conservative force is equal to the reversible work done on or by a system. But since the potential of a conservative force is represented by a point function, this would seem to ...
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2answers
106 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?
2
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2answers
83 views

Accessibility by reversible processes and the Second Law of Thermodynamics

One common way of motivating the existence of Entropy as a state function is the following. Let us take the Clausius/Kelvin-Planck statement of the second law, from which we can deduce Clausius' ...
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4answers
166 views

Does a reversible heat engine exchanging heat with an ideal gas that does a transformation imply that transformation is reversible?

Consider a reversible heat engine working between two sources. Suppose that one of the sources is a thermostat, while the other is an ideal gas which follows a transformation and exchanges some heat ...
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2answers
59 views

Reversible processes in which mechanical or thermal equilibrium is not reached

The definition of a reversible thermodynamic process requires in any instant the mechanical equilibrium (equal pressures) and thermal equilibrium (equal temperatures) of the system in a quasi-static ...
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3answers
178 views

Why is the net entropy change of an irreversible engine positive?

In a Carnot engine the net entropy changein a cycle is zero. But in an irreversible engine operating between two temperatures the net entropy change in a cycle is positive. As I have understood, this ...
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4answers
139 views

Could you filter coffee back to being pure water?

Okay, so coffee filters remove solid matter from the beverage, whilst leaving the remaining coffee intact for caffeiney goodness. But it's got me thinking. Is there a way we could filter the coffee ...
2
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2answers
54 views

Does a circularly polarized electromagnetic wave transfer angular momentum from the transmitter to a receiving antennae?

This question is about the rotation of macroscopic objects and looks at the magnetic vector of an electromagnetic wave. As basis for comparison, we consider an induction motor. The stator induces a ...
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2answers
56 views

Carnot engine basics?

A line in my textbook says.. ' if we employ any other process that is not adiabatic, say an isochoric process, to take the system from one temperature to another, we shall need a series of ...
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1answer
59 views

Entropy and Clausius inequality

From the Clausius inequality we can derive that the efficiency of a Carnot (reversible) cycle is given by: $$e= 1 - \frac{T_c}{T_h}$$ Is this true for every reversible cycle? Is the efficiency of all ...
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3answers
69 views

Does “IF isentropic THEN reversible” only holds for adiabatic processes?

I know that: IF adiabatic and reversible THEN isentropic First question: does the implication IF isentropic THEN reversible hold for adiabatic processes? Second Question: if yes to the above, are ...
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1answer
71 views

Can an adiabatic, isentropic transformation be irreversible?

My question is very similar to this, but I decided to ask another question because I felt that the problem deserved to be addressed in a more specific and formal way and I also wanted to discuss a ...
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2answers
171 views

Thermodynamic transformation

Why is it that any reversible thermodynamic transformation is quasi-static? Also, why is the converse not necessarily true?
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4answers
110 views

Is it possible for a system to become irreversible?

Imagine a ball bouncing in a box for a long time. We know, there is a certain path it can go to bounce off infinitely (see the image). If it gets to this state, it will never be able to get back again....
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2answers
442 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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3answers
108 views

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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2answers
77 views

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 Q_{...
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0answers
17 views

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 $f(x,...
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2answers
145 views

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: $T_{...
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1answer
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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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1answer
255 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
54 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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3answers
256 views

Not Quasi-static, yet reversible process? Is this a valid example?

Imagine a gas (at room temp. and pressure) enclosed in a thermally insulating spherical container. At some instant, the container instantly expands symmetrically (radially outward) to, say, twenty ...
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1answer
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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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2answers
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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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1answer
64 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
66 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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2answers
72 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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1answer
59 views

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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1answer
105 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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2answers
73 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 https://www.ohio.edu/mechanical/...
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1answer
75 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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1answer
861 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 ...
2
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1answer
233 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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1answer
47 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 $T_A$ ...