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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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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Is Hong–Ou–Mandel effect reversible?

According to Hong–Ou–Mandel effect, two photons coming from the different ports will output by the same port with 2 photons since the cross term is canceled by a 1:1 beamsplitter. Since "light ...
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Work done on system and surroundings in an irreversible adiabatic compression

In an adiabatic irreversible compression process, suppose the pressure P(ext) compresses the piston and does some work say 50J.(50J of energy is lost by surrounding). Since the pressure P(int) is less ...
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Temperature difference in a reversible process

In a reversible process, can the temperature be different between the system and surroundings? If not, how the temperature of the system will rise?
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Reversible adiabatic process insight

How can a reversible adiabatic process (theoretically) be brought about since the system is insulated? A $\mathrm dP$ change in pressure will lead to a $\mathrm dT$ change in temperature thus ...
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Theory about reversible electromotive force generated by radiation?

According to equilibrium thermodynamics, I could conceive a reversible process and get the Thomson relation, but what about considering the electromotive force generated by radiation? Could I also use ...
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Change in internal energy and reversible paths between states

As I understand it, the relation (1) $dU = TdS - pdV + \sum_{i} \mu_idN_i$ always holds, even for irreversible paths. The justification seems to be that (2) "$U, S, V, N_1, N_2, ...$ are all ...
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Is $Q=TS$ valid for externally reversible process or internally reversible process?

For $q=tds$ is this equation valid for externally reversible process or internally reversible process? Like for example a heat transfer process in Rankine Cycle is internally reversible but not ...
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Which temperature is the irreversible Clausius inequality about? (Hotter or colder system? And initial or final?)

Consider a real-life & physically possible scenario in which heat is exchanged between two closed systems at fixed volume. We know that the Clausius inequality for (noncyclic) strictly ...
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If I add one particle to the system at a time, When does the time reversal symmetry breakdown?

Suppose I have a system in my mind which consists of two elementary particles interacting with each other via fundamental interactions. We know that fundamental interactions have $T$-symmetry and ...
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Where does the irreversiblity came from if all the fundamental interaction are reversible? [duplicate]

There isn't too much to explain: We know that all fundamental forces are reversible then where does the irreversibility come from? Edit: The following is edit based on comments: Consider a block of ...
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How can melting of ice be a reversible process when it produces an increase in total entropy?

The melting of ice is a reversible process according to most sources I have seen. However, the melting of ice increases the total entropy of the universe which shouldn't be possible if the process was ...
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Reversible processes do not change the entropy of the universe. What is with exergonic reactions? [closed]

I have read that in a reversible process, entropy can be transferred but not generated. Such that the entropy of the universe stays constant. On the other side, there is the Gibbs Energy, which can be ...
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Is it always true that a non-adiabatic reversible process is an isothermal process?

In a Carnot Cycle, a reversible isothermal process is a non-adiabatic reversible process. Is it always true that a non-adiabatic reversible process is an isothermal process?
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Heat differential in irreversible process – what object is it mathematically?

In Thermodynamics, when we talk about quasi-static reversible processes, we often formalize them this way: we identify the state space with a simply connected manifold. On it we have two 1-forms, $đQ$ ...
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Otto cycle reversible or not?

In my course it states that the Otto cycle is an irreversible process. I'm not really sure why. I have also found by a quick google search that a lot of people say the cycle is reversible. To my ...
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Reversible processes

I am now reading about how to calculate entropy changes of a system undergoing a process, and the textbook says that to be able to calculate such a change, you need to imagine that the system is ...
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Is supercooling water reversible?

Water can exist in a supercooled state. Even at $-48,3$ degrees Celsius it can be liquid. Below that temperature, the water will freeze. If I cool the ice to, say, $-60$ degrees and heat it slowly ...
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Why are Reversible Processes quasi-static?

I have heard that all reversible processes are quasi-static but I have not yet found a strong reason for the fact that no non-quasistatic process is reversible. I have seen on some other answers that ...
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How to connect the concept of micro-reversibility with entropy production?

I am confused about the concepts of micro-reversibility and entropy production and how they go together. In the micro-canonical ensemble (constant total energy), the entropy becomes maximal at ...
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Why is the Work Done indeterministic when we know $∆V=0$?

Given: In a process on a closed system in closed container, the initial pressure and volume are equal to the final pressure and volume. Comment about the Net Work Done by the System, Net Heat given to ...
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Violation of the 2nd law of thermodynamics?

According to the second law of thermodynamics, the product of a system's temperature and change in entropy is greater than or equal to the heat supplied to the system, equality if and only if the ...
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Irreversible State Change

When we have irreversible state change than at every point during that change it is said that pressure inside a system is not determined or known and because of that it is impossible to represent ...
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How can The expression $dH = TdS + Vdp$ hold for non-reversible process?

From what I have found online the equation $dH = TdS +Vdp$ holds as all the variables are state variables and the derivation of this just requires $dU = TdS - pdV$ which is valid in all processes (...
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Why does the answer here use $ \Delta S=Q/T$ even though this isn’t reversible? [closed]

This question for my thermodynamics course ends up using $\Delta S = Q_{\text{waste}} / T,$ but I was taught that $ \Delta S=Q/T$ is only valid if the process is reversible. The question makes it ...
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Help with different formulas for Gibbs free energy

I am very confused with the following concepts: Gibbs free energy tells us about the chemical energy of our systems! $$dG=\sum_i\mu_idn_i\qquad\qquad\qquad G=\sum_i\mu_in_i$$ All chemical systems ...
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How to calculate path-dependent integrals in thermodynamics (from 3D simulation results)?

I would like to calculate some path-dependent thermodynamical quantities from the results of a fluid dynamics simulation (single fluid, single phase). One of these quantities is the head $$y_{12} = \...
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Why change in entropy in reversible adiabatic process is zero?

In the adiabatic expansion step of carnot cycle, adiabatic change is carried out in an insulated system. In this process volume gets increased but entropy remains constant. Now if we look at the ...
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Understanding Clausius' inequality for irreversible process

Consider a system which is initially at a state $A$. Then it is moved to state $B$ absorbing $Q_h$ amount of heat from a heat reservoir at $T_h$. As the process is reversible so during heat exchange, ...
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Adiabatic expansion, irreversible, in a container?

I'm reading D. F. Lawden, Principles of Thermodynamics and Statistical Mechanics, and am trying to understand the first worked problem they have. Below is the ...

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