All Questions
264 questions
0
votes
1
answer
14
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Difference in efficiency of isobaric reversible and irreversible process [closed]
I know that the efficiency of a process depends on the reversibility of the same process. When the process is reversible, the efficiency is the highest. Although I don't understand how this works for ...
0
votes
1
answer
72
views
Entropy in a thermally isolated system
In page 141 of the book "Concepts in thermal physics" it is said that for a thermally isolated, the change in entropy is bigger or equal to 0 since $dQ=0$.
But since the system is thermally ...
- 11
3
votes
3
answers
81
views
Equilibrium in a reversible process
My lecture notes state the following (albeit in a very hand-wavy way):
If we
are gentle and careful however, we can change the state of the system slowly, making sure that while
the state is changing ...
- 33
1
vote
1
answer
47
views
Quasistatic and Reversible thermodynamic processes
A quasistatic process is a process where all intermediate states are in equilibrium. A reversible process is a process where no entropy (of the universe) is generated (and thus can be reversed to its ...
-1
votes
3
answers
290
views
The development of Clausius Inequality
The reversible cyclic device absorbs $\delta Q_R$ from the thermal reservoir at $T_R$ and rejects heat $\delta Q$ to the piston-cylinder device, whose temperature at that part of the boundary is $T$ (...
- 105
5
votes
3
answers
139
views
Why is the entropy change for a system in irreversible transformations the same as in reversible transformations in some cases, not in other cases?
Generally, the entropy change for a closed system for an irreversible transformation is not the same in a closed system for a reversible transformation.
A clear counterexample is that of an adiabatic ...
- 1,723
1
vote
2
answers
101
views
Clarification on 2nd law of thermodynamics
I was reading Feynman lectures on the 2nd law of thermodynamics
Now, what about the second law of thermodynamics? We know that if we do work against friction, say, the work lost to us is equal to the ...
2
votes
2
answers
417
views
Can two different points can be connected by multiple adiabatic curves?
I was watching this Thermodynamics lecture and I have a question on the 1st law. More exactly on how different adiabatic curves can connect the same initial and final states. See the diagram drawn at ...
- 1,131
0
votes
1
answer
62
views
Confusion regarding the equation $dS=\frac{\delta Q_{rev}}{T}$
In Reif's Fundamentals of Statistical and Thermal Physics he outlines a "proof" (sections 3.8 and 3.9) of the equation $dS=\frac{\delta Q}{T}$ for any quasi-static, infinitesimal process (i....
- 291
0
votes
1
answer
49
views
Feasibility of entropy at zero temperature
I remember a college lecturer of mine once gave me this equation of entropy during one of his lectures on thermodynamics:
$$
\begin{align*}
\Delta{S} = \frac{ d {Q} }{T} \\
\end{align*}
$$
I found out ...
- 41
0
votes
1
answer
81
views
Is the 2nd law a reason for the irreversibility of natural processes or a consequence of it?
I have been introduced to chemical engineering thermodynamics due to my academic background. I had learnt about internal energy, entropy etc and applied the equations to various scenarios of practical ...
- 1
0
votes
1
answer
64
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Entropy in irreversible adiabtic process
We know that,
$$dS=\dfrac{\delta Q_{rev}}{T}$$
If you have an irreversible adiabatic process between two thermodynamic equilibrium end states of a system, there exists no possible reversible adiabatic ...
6
votes
5
answers
675
views
Use of Clausius theorem to prove entropy inequality in Fermi's Thermodynamics
At the beginning of Section 13 (at the bottom half of page 54 through the top half of page 55) of Enrico Fermi's classic Thermodynamics, he sets out to prove the relation (using his notation)
$$S(B) - ...
- 105
1
vote
1
answer
108
views
What is the relationship between Clausius Inequality and 2nd Law?
I am confused about the application of the 2nd Law for reversible and irreversible processes and cycles.
I want to know how the Clausius principle, the Kelvin-Planck statement, and the Clausius ...
- 31
2
votes
2
answers
106
views
What is the difference between a reversible process and an equilibrium? [closed]
I am confused about the differences between a reversible process and an equilibrium when considering their energy aspect.
Here is what I know so far.
(1) Equilibrium and Reversibility
Equilibrium ...
- 31
0
votes
1
answer
210
views
Change in entropy in reversible and irreversible process
Let's take a process with constant pressure in ideal gas for example. in reversible process
$dS=\int_{1}^{2}\frac{\delta Q_{rev}}{T}=\int_{1}^{2}\frac{C_pdT}{T}$
Assuming constant specific heat ...
- 11
1
vote
2
answers
228
views
Change of entropy of irreversible and reversible processes and cycles
Clausius' theorem states that
$$\oint\dfrac{\delta Q}{T}\leq 0,$$
$=$ for reversible cycles and $<$ for irreversible ones.
For a cycle with two reversible paths connecting points $a$ and $b$,
$$\...
- 420
0
votes
1
answer
35
views
Reversible processes in thermodynamics [closed]
These are a few basic questions of mine in thermodynamics whose answer I can't find anywhere.
$1$. How does a quasi static process serve the purpose of thermodynamic equilibrium?A quasi static process ...
- 379
0
votes
2
answers
159
views
How do I find the entropy change of the universe for a not-completely-irreversible isothermic expansion?
My chemistry professor recently showed this in a presentation explaining thermodynamics. In particular, he used it as a demonstration that global entropy rises when starting from the assumption that ...
- 3
1
vote
2
answers
121
views
Change in entropy for a reversible process
The infinitesimal change in entropy of a reversible process is given by $\text{d}S=\frac{\delta Q}{T}$. How is this proven?
For a measurable change, $\Delta S = \int_{1}^{2} \frac{\delta Q}{T}$.
I'...
4
votes
2
answers
217
views
Increase of entropy when two reservoirs are in thermal contact
While reading my textbook , I came across a proof which intended to verify that entropy always increases when a hot reservoir is kept in thermal contact with a colder reservoir.
The proof goes as ...
- 109
1
vote
2
answers
447
views
Intuitive explanation for reversible and irreversible process
I have read that a reversible process is one in which $\Delta S_{\text{universe}}=\Delta S_{\text{system}}+\Delta S_{\text{surroundings}}=0$ and an irreversible process being one in which $\Delta S_{\...
12
votes
10
answers
6k
views
Why don't the first two laws of thermodynamics contradict each other?
The second law of thermodynamics states that the entropy of the universe increases over time and this has lead to theories like the heat death of the universe and the big rip. What this means in ...
- 255
0
votes
4
answers
290
views
Heat being transferred from colder object to hotter object
My son was watching a YouTube video on entropy (The Most Misunderstood Concept in Physics). At about 11:30, it said that in theory it is possible to observe, say, "heat" moving from colder ...
- 313
0
votes
2
answers
79
views
Why the insistence that the process be reversible for $dW_{RWS} = -dF$ to hold (Helmholtz free energy)?
In a discussion about the (change in the) Helmholtz potential being interpretable as the maximum available amount of work for a system in contact with a thermal reservoir (i.e. the free energy), ...
- 1,271
2
votes
1
answer
115
views
How to know when a reversible process between end states exists?
I am continuing to try to understand maximum work reversible processes (and a subset thereof -- Carnot cycles) better. I am here curious about the following system.
(1) Consider one mole of a gas (...
- 1,271
0
votes
1
answer
168
views
Callen's Maximum Work Theorem: why doesn't heat lost equal heat absorbed (and likewise for work)?
This question was, effectively, asked here (please refer to that question for additional context); however, I don't think the given answer is correct (or at least complete) despite my having added a ...
- 1,271
0
votes
2
answers
201
views
Why is any real process which proceeds through non-equilibrium states necessarily irreversible?
As per the title, why is any real process which proceeds through nonequilibrium states necessarily irreversible?
The question came up when reading Callen's definition of "reversible process" ...
- 1,271
2
votes
4
answers
95
views
Reversibility and its surroundings
I was thinking about the definition of reversibility but there is something that I cannot understand. In real life the surrounding of a system (anything else in the universe) is always changing making ...
- 51
-1
votes
1
answer
959
views
Please explain why the Carnot cycle is reversible while the Otto cycle is irreversible using the kelvin or clausius statement of the second law [closed]
why is the Carnot cycle reversible while the Otto cycle irreversible according to Kelvin-planck statement
- 41
-1
votes
1
answer
74
views
What does $Q$ refer to in this inequality $\Delta S\ge\frac{Q}{T}$?
Entropy change of a system due to heat $Q$ can be expressed by the following inequality (assuming that temperature is constant):
$$\Delta S_\mathrm{sys}\ge\frac{Q}{T} \tag{1}$$
It can be expressed ...
- 205
2
votes
1
answer
761
views
How it is possible for entropy of universe to increase during reversible process?
To calculate the entropy change of the universe when a closed system undergoes an irreversible process, one must choose a reversible process and calculate the following integral
$$\Delta S=\int \frac{\...
- 205
-4
votes
4
answers
182
views
Derive $ΔS = Nk\ln(V/V_0)$ using fundamental equations of thermodynamics [closed]
I am considering a system with an ideal gas undergoing an adiabatic expansion. The initial volume is $V_0$ and final is $V$.
From this, How do I derive $\Delta S = Nk\ln(V/V_0)$ using fundamental ...
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0
votes
1
answer
95
views
Entropy change in heated block [closed]
The header of the problem asks us to calculate the entropy change $\Delta S$ (in the universe) when heating an iron block from $T_1$ to $T_2$, knowing its heat capacity $C_V$. Is it possible to ...
2
votes
2
answers
111
views
Does the rate of heat addition to a thermodynamic system affect its final state?
I have read that the entropy change of a system is greater than or equal to the integral of the heat added to it divided by its temperature. The case where entropy is equal to the integral is when the ...
- 109
0
votes
1
answer
240
views
Free energy change in reversible/irreversible processes
Yet another follow up to this question,
I am struggling to understand the example provided in Chet Miller's answer:
An example of this is expansion of an ideal gas in contact with an ideal constant ...
- 205
12
votes
2
answers
2k
views
Difference between Reversible and Irreversible processes in Physics vs. Chemistry
In Physics a reversible process is defined as one in which the system can be returned to its initial conditions via the same path (along the PV Diagram), and every point along the path is an ...
- 123
0
votes
0
answers
95
views
Can someone explain this to me? About reversible computing with finite energy and thermal equilibrium
In Life, The Universe, and Nothing: Life and Death in an Ever-Expanding Universe, they examine the implications of dark energy on the ultimate fate of life.
Then they say this,
It was long thought ...
- 39
0
votes
3
answers
225
views
$dq_{rev}$ and $dq$, which one is larger? [closed]
Im learning about entropy and some concepts makes me confusing.
For a reversible and irreversible process with a same initial state and final state, it is said that entropy change of a system is ...
- 17
0
votes
1
answer
36
views
Reversible thermodynamics processes
A problem asks me to find the entropy increment in the machine operating some thermodynamic cycle. Can I assume that any closed cycle can (theoretically) be obtained by using two reservoirs at some ...
- 49
1
vote
3
answers
183
views
A reversible transformation, but there is finite temperature heat transfer?
Suppose to have 3 heat reservoirs, the first at temperature $T_1$, the second at temperature $T_1+dT$ and the third at temperature $T_2>T_1$
Then, consider a system, which volume is constant, in ...
- 1,978
1
vote
4
answers
1k
views
Why can't a heat engine have 100% efficiency?
Using the idea of isotherms and adiabats, I came up with the following argument to convince myself. First imagine the working gas within the system being heated along an isochore (hence all heat ...
- 75
0
votes
3
answers
749
views
How can the Entropy (change in entropy) of reversible and irreversible process be the same? If Entropy of reversible process is 0
E.g., the change in entropy of a reversible process 0, then irreversible process should have 0 change in entropy. This question arose because I couldn't understand why generally work done by ...
- 15
0
votes
1
answer
173
views
What is Entropy Balance Relative to (un)Compensated Heat of Clausius?
Consider the ideal Carnot cycle consisting of two ideal reversible isothermal stages at $T_0$ and $T_1$ and two ideal adiabatic reversible (isentropic) stages connecting them; assume that $T_0 > ...
- 20.4k
-2
votes
1
answer
73
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Are there any time irreversible processes on earth which aren't due to the sun?
The sun is very hot. The earth is cold. Energy always flows from hot to cold systems. Due to the temperature difference, useful energy can be imparted onto earth (i.e., blackbody radiation from the ...
- 11.8k
2
votes
3
answers
145
views
How do I prove reversible transformations are necessarily quasistatic without using entropy?
I have the following definitions:
A transformation is said to be quasistatic if it passes only through equilibrium states (that is, the thermodynamical coordinates of the system are defined at every ...
1
vote
2
answers
195
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Understanding page 141 of Blundell’s Concepts in thermal physics
On this page (in the second edition), there is a figure containing two states A and B of a system:
There are two paths between A and B: one is an irreversible change, and the other is a reversible ...
- 1,502
6
votes
5
answers
1k
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Why isn't the free expansion of a gas in an adiabatic container isentropic?
If you expand a gas adiabatically using a piston, the process is isentropic. However, if you simply remove the piston and let the gas expand freely, the process is now not isentropic. What makes these ...
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3
votes
1
answer
365
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Proof of Caratheodory's theorem
Caratheodory's formulation of second law of thermodynamics, also referred to as Caratheodory's principle states
In any neighbourhood of any thermodynamic state $P$ there exist states which are ...
- 311
2
votes
4
answers
134
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Fundaments of thermodynamics and separating entropy
I tried to write down my "own" fundamental rules of thermodynamics, which I can then use as solid ground to understand the rest of the topic. The main thing I thought of is separating ...
- 21