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 don't we call this irreversible?
I've read that a quasi-static process in which entropy change only because of heat exchange: $\Delta S=\int \frac {\delta q} T$ is not called irreversible. The name irreversible is reserved for ...
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Reaction to increase and diminish mass at will (forward and reverse reactions) [closed]
Non-professional question... Is there currently a method for converting mass to/from another form of energy? This would be like an exothermic reaction in that mass is consumed, but it would also have ...
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Adiabatic free expansion (Joule expansion) needing a small explanation
My professor tries to demonstrate that adiabatic free expansion is an irreversible process:
for and adiabatic $Q=0$;
because the gas is expanding through vacuum W=0;
therefore $\Delta U=Q-W=0$
now ...
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Why does entropy jump across a shockwave?
Using the Rankine-Hugoniot relations for a shockwave, one can show that entropy jumps across the shock, so that the entropy difference between upstream and downstream conditions is given by
$$s_2 - ...
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Entropy Change - which formula to use?
I am looking at a system of two solids A and B, that is isolated.
A is at a higher temperature; thus, we have heat transfer from A to B.
If I wished to calculate the entropy change:
$$\Delta S_{tot} = ...
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Heat transfer from, or to, a large heat reservoir is always reversible?
A heat reservoir (Figure above) is a constant temperature heat source or sink. Because the temperature is uniform, there is no heat transfer across a finite temperature difference and the heat ...
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In a reversible heat exchange, does the system and reservoir need to almost have the same temperature?
In order for a process which involves heat flow from surroundings to the system to be reversible, is it necessary that the temperature difference between the system and surroundings be very small at ...
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What is the difference between irreversible and reversible isochoric processes done on an ideal monatomic gas in a frictionless system?
Suppose we had two thermal reservoirs at $T_{c}$ and $T_{h}$ with $T_{c} < T_{h}$ and an infinite series of thermal reservoirs with a continuous range of temperatures between $T_{c}$ and $T_{h}$.
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What's the significance of a quasi-static process?
Is there a problem, if my thermodynamic process is not quasi-static?
I have read the definition that a quasi-static process is an infinitesimally slow process in which every intermediate state of a ...
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Is the increase of entropy a theorem?
Let us consider an isolated system of $N$ particles whose motion is determined by Newtonian mechanic, over time that stretches from $-\infty$ to $+\infty$. The system is isolated, therefore the only ...
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Reversible vs Irreversible process
A Hypothetical Situation:
Two thermally isolated identical systems have heat capacities which vary as:
$$Cv =βT^4$$($β$ is constant)
Initially one system is at $300K$ and the other at $400K$. The ...
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Meaning of "Heat engine working between two Temperatures"
According to Carnot Theorem:
"Of all engines working between two given temperature, none is more efficient than a carnot engine."
I want to know what actually is meant by an engine working ...
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Is the enthalpy change in a reversible adiabatic expansion of an ideal gas 0?
I would like to know what happens to the enthalpy in a reversible adiabatic expansion for an ideal gas. Will it be greater than or equal to zero?
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Proving that the diffusion equation is not time-reversible
The diffusion equation (in appropriate units) is
$$
\frac{\partial\rho}{\partial t}(\mathbf r,t)=\nabla^2\rho(\mathbf r,t).
$$
By time-reversibility, I mean that there exists a function (bijection?) $...
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Sudarshan's dynamical maps
This is a question about an equation in a paper by E.C.G. Sudarshan, P.M.Matthews and J. Rau. The authors introduce the concept of dynamical maps - objects that determine the time evolution of density ...
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Reversible Or Irreversibile
If we know the path on P-V diagram, are we definitely sure that the process, in general, is reversible ? For example, we consider that the engine cycles are reversible, is it because we know the path?
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Adiabatic process and internal energy
My question concerns the connection between change in internal energy $dE = Q - W$ and the available work in an adiabatic process.
My understanding is, that in an adiabatic process ($Q=0$) the change ...
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Questions regarding quasi-static and reversible processes
There are various things I am not sure I fully understand regarding reversible and quasi-static processes. I have tried to find similar questions on this forum, but so far none have fully answered my ...
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Entropy and Irreversibility
I was watching Tenet and it made me think about some old questions I have. The second law of thermodynamics states that in every thermodynamics process, the variation of the entropy of a closed system ...
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Carnot cycle total reversibility
I read the discussion of the same problem in another problem posted here Carnot Total Reversibility, but still I can't get the reason why Carnot cycle is stated as "Totally Reversible", it ...
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Why pressure increases in a piston-cylinder device in isothermal reversible expansion?
A piston–cylinder device contains 1.2 kg of saturated water vapor at 200∘C. Heat is now transferred to steam, and steam expands reversibly and isothermally to a final pressure of 800 kPa. Determine ...
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Isothermal heat transfer processes are always reversible?
in my textbook, it is mentioned ;
" isothermal heat transfer processes are internally reversible "
what is the reason behind that?
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Simplest possible thought experiment that illustrates the difference between the past and the future?
We are led to believe that the "arrow of time" is determined by the direction in which entropy increases. Entropy is a measure of disorder, but disorder is very much in the eye of the ...
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Why can't complete heat be converted to work if its vice versa is possible?
Is there any proof of why complete heat connot be completed to work rather than the second law of thermodynamics. It might be possible that we are not able to process the heat to complete work at this ...
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Why entropy change of reservoir is reversible?
When two reserviors exchange heat, it is considered as reversible heat transfer and entropy is calculated.
But when the process is reversible change in entropy of universe must be zero. But why ...
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Why can we get maximum work from a reversible process?
We know that the work done by any force is independent of the speed of the object and it depends only on the force and displacement.
So if we consider a close gaseous system with a movable piston ...
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Difference Between Molecular Dynamics and Kinetic Theory? Loschmidt's
Disclaimer : Im not a physicist!
I have heard Loschmidt's paradox described as "the laws of thermodynamics are time asymmetric because entropy always increases, but the underlying laws of physics ...
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How can we say that entropy is constant if and only if all processes are reversible?
The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time, and is constant if and only if all processes are reversible.
For an isolated system, ...
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Entropy and Heat Conduction
For an Intro. Thermal Physics course i am taking this year, I had a simple problem which threw me off-guard, I would appreciate some input to see where i am lacking. The problem is as follows:
Does ...
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What's the difference between burning a book and throwing it into a black hole [duplicate]
There is a big concern about loosing information inside a black hole. As far as I understand, the black hole is characterized classically by its mass, angular momentum and charge. Semi-classically, ...
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From where does irreversibility arise in the Navier-Stokes momentum equation?
A form of the Navier-Stokes momentum equation can be written as: $$ \rho \left( \frac{\partial \mathbf{u}}{\partial t} + \mathbf{u} \cdot \nabla \mathbf{u} \right) = - \nabla \bar{p} + \mu \, \nabla^2 ...
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Can I assume that steam leaking from a rigid insulated tank is an isentropic process?
I’m trying to solve this problem. If you have a rigid insulated tank with $V=10\ {\rm m}^3$ which is initially filled with steam at $p_1=0.7\ {\rm MPa}$ and $T_1=240\ {\rm C}^\circ$. The tank develops ...
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Can a non-unitary free operation on a resource state be reversed?
Under the framework of resource theories like entanglement, asymmetry, athermaility, etc, a set of operations $\mathcal{O} \subset \mathcal{B}(\mathcal{H})$ is chosen (e.g., LOCC) due to physical ...
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Big crunch theory
We study in thermal physics that no natural processes are reversible i. e. they are irreversible, so size of universe, it's also natural process. Why we still say big crunch theory a theory, why can't ...
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General definition of reversible process without mentioning changes in the environment
I'm looking a general definition of a reversible process for a (closed) system that wouldn't need to say anything about the environment and would be based on the intuitive notion of "reversing&...
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Reversibility of Physical Process : QM vs CM
It is often stated that the processes in quantum mechanics are reversible as they follow the Schrodinger's Equation : $$ - \frac{\hbar^2}{2m} \nabla^2 \Psi(x,t) + V(x,t)\ \Psi(x,t) = i \hbar\ \frac{\...
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Definition of reversibility for a non-adiabatic process
I would like to find a clear definition for the following expression:
System A undergoes a reversible transformation
when the transformation is not adiabatic (when system $A$ is not thermally ...
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Is a constant pressure adiabatic irreversible expansion possible?
We know that adiabatic law for an ideal gas is,
$$ PV^{\gamma} =C$$
the differential of this under constant pressure is,
$$ P \gamma V^{\gamma-1} dV = 0$$
Now, the pressure and volume can't be at all ...
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What features do reversible work have over the irreversible kind?
At 6:47 of this video lecture, the professor defines enthalpy for a constant pressure process as
$$ q_{p}= \Delta U + p \Delta V$$
but, I can not understand why the work he implicitly starts referring ...
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What dependence does reversibility have on the time taken to change state of a system?
In this video lecture , at 39:37, The professor describes that if we do the process slowly then the system moves through a set of equilibrium states but why exactly does the speed of doing the process ...
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Two Polytropic and Two Adiabtic processes in Thermodynamic cycle [closed]
$1$ mole of an Ideal gas performs a reversible cycle with 2 adiabatic and 2 polytropic processes.
$A(P_0,V_0,T_0)$ to $B$ with $V_B=V_A/\lambda$ with an adiabatic process.
$B$ to $C$ with a polytropic ...
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Do irreversibilites change the final temperatures of two bodies?
When two identical bodies are brought into thermal contact, and both are surrounded by an isolation, does the fact that they have a finite temperature difference, which generates entropy, change their ...
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Why are simple models of coupled pendulums incapable of describing irreversible energy dissipation?
Consider two pendulums $A$ and $B$ coupled by a spring and also regard $A+B$ to be a completely isolated system. Let us start the system in an initial configuration where only one of the pendulums (...
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Why is the work done in reversible process greater than work done in irreversible process?
I have read in my textbook that maximum work is done by gas in a reversible expansion, but I do not know the reason behind it.
Also is work done by gas maximum in reversible compression also?
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Examples of processes that are reversible isentropic but not adiabatic?
Since $ds=\frac{dq_{rev}}{T}$ for reversible processes it seems we can have reversible isentropic processes that are not adiabatic provided the temperature changes in such way that the sum of $\frac{...
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How does the reversibility of physics interact with nuclear fission?
The laws of physics are reversible and quantum information is never destroyed.
Given this, how do I time reverse the $U_{235}$ fission reaction, n which
${}^1_0n + {}^{235}_{92}U \rightarrow {}^{141}_{...
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How to find the maximum work that can be extracted by two objects which have variable temperatures?
How to find the maximum work that can be extracted by two objects which have variable temperatures $T_1$ and $T_2$ with $T_1 > T_2$?
I've thought that the maximum work obtainable is the one ...
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Conditions for a process to be quasistatic, non-quasistatic, reversible or irreversible
I have a little mess with the conditions required in thermodynamics for a certain process to be quasistatic, non-quasistatic, reversible or irreversible.
Let's start with the classification of the ...
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Why the reversibility requirement in Clausius equality doesn't prevent defining the entropy from it?
In his original work Clausius defines the entropy from his equality $\oint \frac{\delta Q}{T}=0$, which holds for a reversible cyclic process. As it means the integral $\int \frac{\delta Q}{T}$ over a ...
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Obtaining the direction of flow from principle of increase of entropy?
Can we mathematically show that water flows from high-pressure region to low-temperature region and why particles flow from a region of higher chemical potential to lower on the basis of the principle ...
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