All Questions
Tagged with irreversible or reversibility
130 questions
8
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Assumptions of thermodynamic & chemical equilibrium in fluid-dynamics
I am reading about the Euler equations of fluid dynamics from
Leveque's Numerical Methods for Conservation Laws. After introducing the mass, momentum and energy equations, some thermodynamic concepts ...
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26
votes
6
answers
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Is there a quasistatic process that is not reversible?
I have seen several questions and good answers on the link between reversible and quasistatic processes, such as here or here. However, these questions only adress one side of the problem : a ...
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15
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11
answers
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Where does the irreversiblity came from if all the fundamental interaction are reversible?
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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10
votes
1
answer
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A thermodynamic transformation that can be represented by a continuous quasistatic path in its state space may still be irreversible. Why?
A thermodynamic transformation that has a path (in its state space) that lies on the surface of its equation of state (e.g., $PV=NkT$) is always reversible (right?). However, if the path is a ...
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7
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2
answers
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Difference between irreversibility and entropy?
Cedric Villani recently wrote an article on Landau damping in collisionless plasmas, where at least one topic discussed confused me. Besides discussing the issue of how a process can be ...
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2
votes
1
answer
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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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0
votes
1
answer
596
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Work done by a gas in an isothermal process
So the equation for reversible work is $xRT \sim \ln\left(v_2/v_1\right)$ where $x = \textrm{no. of moles of gas}$. This is calculated on the basis of internal pressure. This equation is also given ...
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4
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How is entropy a state function?
Is there only one reversible way to move from one state to another?
If we consider two states $A$ and $B$ on an isotherm and we move from $A$ to $B$ by first reversible isochoric process and then ...
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15
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5
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Intuitively, why is a reversible process one in which the system is always at equilibrium?
A process is reversible if and only if it's always at equilibrium during the process. Why?
I have heard several specific example of this, such as adding weight gradually to a piston to compress the ...
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4
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1
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How does Fermi jump to this conclusion in Clausius inequality?
In his $Thermodynamics$, Fermi proves beautifully the following (rephrased):
For a system undergoing a cyclic process, $$\oint {\delta Q\over T}\leq 0,$$ and for a reversible cyclic process, it is ...
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3
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3
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What ds>dQ/T mean?
I read the derivation on page 216 over here.
First, it considers an irreversible process between states 1 and 2, followed by a reversible process between states 2 and 1.
From my interpretation, ...
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2
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1
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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 ...
user36790
20
votes
4
answers
2k
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Hawking radiation and reversibility
It's often said that, as long as the information that fell into a black hole comes out eventually in the Hawking radiation (by whatever means), pure states remain pure rather than evolving into mixed ...
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15
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6
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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:
$T_{...
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4
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Is heat death reversible by thermal or quantum fluctuations given an infinite time?
I'm new here, so apologies if the question doesn't sound meaningful considering what physics is supposed to answer. I don't have a physics or mathematics background, but I did learn a few things about ...
- 452
9
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3
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Quasistatic vs Reversible processes
Would it be fair to state the difference between quasistatic and reversible processes as follows?:
A process is quasistatic if at every point in the process the system is in equilibrium with itself.
...
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4
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In the Langevin dynamics: neglecting inertia. A mathematician trying to understand physics terminology
If we write the Langevin equation: for a particle with mass $m$, position $x$ and velocity $v$, with some damping coefficient $\gamma$,
$$ m dV(t)=-\gamma V(t)dt+dW(t) ,~~~~~~~dX(t)=V(t)dt.$$
Then as $...
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4
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2
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606
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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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3
votes
3
answers
3k
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Entropy and reversible paths
I'm a little bit confused about calculating entropy changes along irreversible paths by integrating over a reversible path. When using the central equation I can understand the argument, entropy and ...
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2
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Can anyone prove this overstated-but-almost-never-justified fact from thermodynamics?
Clausius inequality states that $\oint {\delta Q\over T}$ equals zero for a system undergoing a reversible cycle, whereas it can’t be greater than zero for an irreversible cycle.
But everywhere, I ...
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22
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4
answers
3k
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How slow is a reversible adiabatic expansion of an ideal gas?
A truly reversible thermodynamic process needs to be infinitesimally displaced from equilibrium at all times and therefore takes infinite time to complete. However, if I execute the process slowly, I ...
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18
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1
answer
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Principle of Caratheodory and The Second Law of Thermodynamics
Background
Constantin Carathéodory formulated thermodynamics on a purely mathematical axiomatic foundation. His statement of the second law is known as the Principle of Carathéodory, which may be ...
- 2,166
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8
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How is this process not quasi-static yet reversible?
Consider a (adiabatic) canister with a piston containing some gas kept in a vacuum. There are two weights on the canister which equalize the pressure of the gas on the piston. Assume the system is at ...
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2
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3k
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Hysteresis and dissipation
Hysteretic phenomena are often linked to dissipation. When there is a hysteresis loop, the dissipated energy can usually be computed as the area of the cycle.
For example, in ferromagnetic materials, ...
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12
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1
answer
3k
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What are entropy and reversible processes really?
I'm confused about the concepts of entropy and reversible processes.
Before explaining the definition of entropy, they used the term "reversible process" without defining it formally. Then, when ...
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4
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Why is work done equal to $-pdV$ only applicable for a reversible process?
In thermodynamics, when we're interested at gases, I know that the work done can be written to be $-pdV$ for a reversible process ($p$ is the pressure of the system, and $V$ is the volume of the ...
user148792
7
votes
5
answers
1k
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Reversible vs Quasistatic
I have some confusion about the definitions of a quasi-static and a reversible thermodynamic transformation.
As far as I understand, a quasi-static process is one that happens slowly enough for the ...
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7
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1
answer
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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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7
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3
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3k
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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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2
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What is the difference between reversible and irreversible adiabatic expansion?
What is the difference between reversible and irreversible adiabatic expansion?
Is it true that the work done by the gas is the same but the pressure applied externally differ between two process?
If $...
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5
votes
1
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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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5
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2
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Entropy change in reversible and irreversible processes
$dS = dq/T$ for a reversible process and $dS \gt dq/T$ for an irreversible process, but why is the entropy change greater in an irreversible process? What difference between the two processes in ...
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1
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What is the reason of hysteresis loss?
Consider a ferromagnetic material is subjected to a gradually increasing external magnetic field and magnetized to saturation. Then a reverse field is applied to demagnetize the material and then the ...
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4
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3
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Meaning of reversibility and quasistatic processes
A process in a closed system is reversible if the entropy change is $dS = \frac{dQ}{T}$.
A process is quasistatic if a process is infinitely slowly.
Now, if a process is reversible, this means ...
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4
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0
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48
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Why Onsager's formulation of thermoelectricity is better than Bridgman's?
General comment: despite the longish historical introduction this question is not about the history of physics but rather about a specific conceptual problem in physics.
Following Bridgman in the ...
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4
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2
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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
$$s_2 - ...
- 2,659
4
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2
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496
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Entropy: subjective lack of knowledge that leads to objective conclusions
There is something I really don't get about entropy.
Let's consider a classical system (not quantum mechanics here).
We can compute the entropy of a system via the formula $$S=-\sum_l P_l Log(P_l)$$ ...
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3
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2
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Work done by reversible and irreversible process
Reversible work is greater than irreversible work and the examples given in the book are isothermal reversible work and isochoric irreversible work. The explanation is as following.
"More work is ...
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2
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Reversibility in classical mechanics
I am watching Susskind's 'Theoretical Minimum' videos. At one point in his course on classical mechanics (2nd video if I remember correctly) he affirms that Netwon's second law of motion makes ...
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2
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3
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253
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Why are quasi-static processes reversible? [duplicate]
When a thermodynamic system, like an ideal gas within a piston immersed in a heat bath, is subject to changes, such as compression or extension of the piston, then the work that can be extracted from ...
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2
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2
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97
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Defining reversibility without resorting to entropy
Is it possible to define the concept of reversible process without using any mention to entropy?
The Wikipedia definition of reversible process seems to accomplish this by stating that:
In ...
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4
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251
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Using quasistatic processes to calculate quantities
This question is inspired by Reif Problem 5.5. Note that it is not a homework problem and, even if it were, my question only loosely relates to it.
A vertical cylinder contains $N$ molecules of a ...
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3
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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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1
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3
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854
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Entropy maximum postulate and reversibility
I'm studying Thermodynamics on Callen's book and he introduces entropy through the entropy maximum postulate, namely:
There exists a function (called the entropy $S$) of the extensive parameters of ...
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1
answer
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Reversible and Quasi-static processes
Do we have any proof that reversible processes are always quasi-static or is it just a fact that hasn't been violated till date? If there is a proof then please provide a link.
1
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1
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314
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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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5
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Efficiency of Stirling engine and Carnot's theorem
I want to calculate the efficiency of this Stirling cycle for an ideal gas $pV = nRT$
The mechanical work is
$$
\Delta W_{12} = - \int_{V_1}^{V_2} p(V) \mathrm{d}V = -nRT_2 \ln \frac{V_2}{V_1}\\
\...
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5
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Why do reversible processes not increase the entropy of the universe infinitesimally?
The book Commonly Asked Questions in Thermodynamics states:
When we refer to the passage of the system through a sequence of internal equilibrium states without the establishment of equilibrium with ...
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2
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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 ...
11
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6
answers
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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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