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.

Filter by
Sorted by
Tagged with
1
vote
1answer
72 views

Why does the answer here use $ \Delta S=Q/T$ even though this isn’t reversible?

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 ...
0
votes
0answers
30 views

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 ...
0
votes
0answers
20 views

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} = \...
0
votes
3answers
48 views

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 ...
0
votes
2answers
65 views

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, ...
1
vote
1answer
42 views

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 ...
0
votes
2answers
28 views

How can a system/surrounding never be restored to it's initial state for irreversible cyclic processes?

In a cyclic process, the system returns to the same state i.e. the same $P, V, T$. If this is an irreversible cycle, how can the surrounding not return to it's original state? Wouldn't this imply that ...
0
votes
0answers
29 views

Entropy of Isothermal Expansion

I know that the change in entropy is 0 for reversible processes and is nonzero for irreversible ones. For isothermal free expansion (not reversible) the change in entropy is nonzero (i.e. proportional ...
5
votes
0answers
52 views

Reversibility of light rays, Faraday effect and Fermat's principle

I am currently having some struggle to understand the connection between the following three concepts in optics: Law of Reversibility (Geometrical Optics): The direction of light rays does not matter ...
0
votes
2answers
63 views

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 ...
0
votes
2answers
18 views

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 ...
0
votes
1answer
60 views

Closed system in thermodynamics

If a closed system experiences a new work transfer while it undergoes a reversible process, does a net heat transfer from the system always occur? If not, please provide an example when a net heat ...
0
votes
1answer
56 views

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 ...
1
vote
2answers
40 views

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 - ...
1
vote
3answers
87 views

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} = ...
0
votes
1answer
60 views

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 ...
0
votes
2answers
53 views

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 ...
0
votes
0answers
24 views

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 $T_{h}$. ...
1
vote
1answer
79 views

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 ...
2
votes
1answer
94 views

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 ...
0
votes
1answer
48 views

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 ...
0
votes
1answer
76 views

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?
5
votes
1answer
181 views

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?) $...
4
votes
1answer
121 views

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 ...
1
vote
2answers
39 views

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?
0
votes
2answers
51 views

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 ...
0
votes
1answer
177 views

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 ...
0
votes
0answers
57 views

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 ...
1
vote
1answer
28 views

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 ...
0
votes
2answers
41 views

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 ...
0
votes
3answers
226 views

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?
6
votes
9answers
521 views

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 ...
1
vote
2answers
158 views

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 ...
4
votes
3answers
315 views

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 ...
0
votes
3answers
96 views

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 ...
0
votes
1answer
53 views

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 ...
0
votes
3answers
80 views

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, ...
1
vote
2answers
57 views

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 ...
4
votes
2answers
114 views

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, ...
2
votes
2answers
124 views

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 ...
0
votes
1answer
46 views

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 ...
-1
votes
1answer
78 views

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 ...
0
votes
1answer
34 views

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 ...
0
votes
2answers
46 views

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&...
0
votes
1answer
41 views

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{\...
1
vote
3answers
147 views

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 ...
0
votes
2answers
121 views

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 ...
1
vote
1answer
77 views

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 ...
0
votes
3answers
39 views

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 ...
0
votes
3answers
128 views

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 ...

1
2 3 4 5
9