All Questions
Tagged with reversibility energy
23 questions
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
1
vote
1
answer
115
views
Clarification on the Use of $\frac{dS}{dE} = \frac{1}{T}$ vs. $\frac{dS}{dQ} = \frac{1}{T}$ in Thermodynamics
I'm currently studying thermodynamics and have encountered two expressions relating changes in entropy to temperature, but applied in seemingly different contexts:
$\frac{dS}{dE} = \frac{1}{T}$, ...
- 67
0
votes
0
answers
28
views
Energy spread and reversibility of a thermodynamic process
Recently, while studying thermodynamics I came across something called a reversible process, textbook stated that an infinitesimally slow process can be termed as a reversible process.
This doesn't ...
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
2
votes
3
answers
261
views
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 ...
- 905
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
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
-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
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
1
vote
3
answers
239
views
Why is rapid expansion/compression considered a reversible/isentropic process?
I am looking over the Otto Cycle on this MIT website and it says at one point "the processes from 1 to 2 and from 3 to 4 are isentropic" in reference to the expansion and compression of the ...
- 355
0
votes
0
answers
48
views
Confusion with Gibb's energy [duplicate]
For a reversible process , I can show that $$\mathrm dG=0$$
For the same reversible process I can also prove that $$\mathrm dG=\mathrm dW_{\text{max, non } P-V\text{ work}}$$
Does that imply maximum ...
- 892
1
vote
2
answers
152
views
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 ...
8
votes
6
answers
2k
views
Does bitcoin mining take work?
I'm neither a professional in cryptocurrency nor physics, but an interesting idea occurred to me. Bitcoin involves mining, which generates a lot of heat as waste.
Is the amount of heat produced by a ...
- 2,366
0
votes
0
answers
59
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 ...
- 33
1
vote
1
answer
522
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 ...
- 1,340
0
votes
2
answers
716
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 ...
2
votes
1
answer
61
views
What is the physical interpretation of the Helmholtz free energy for an isothermic, irreversible process?
$$dF=-SdT-pdV$$
For an isotherm, $dF=-pdV$, so $\Delta F=-\int^{V_1}_{V_2}pdV$. Thus, a change in the free energy tells us how much work has been done by or on the system. However, at this point the ...
- 1,327
0
votes
2
answers
734
views
In an irreversible or reversible isobaric process, is $Q$ equal to $dH$? is $dH$ equal to $W$?
First of all,
Is an irreversible isobaric process even considered a truly isobaric process? Or can it be neglected when considering generalized rules for isobaric processes?
Heat added or removed to ...
- 3
2
votes
1
answer
3k
views
Irreversible and reversible compression work
Why is work done on the gas when it is compressed from (p2,V2) (pressure,volume) to (p1,V1) against constant pressure external pressure p1 maximum when it is done irreversibly?
In reversible process, ...
- 309
1
vote
0
answers
52
views
Trying to get one step closer to the understanding of free energies $F$ and $G$
I find it quite hard to get a good grasp of the notions of Helmoltz and Gibbs free energy, because they can be introduced in so many different ways, and embody so many different ideas at once...
Here,...
- 968
7
votes
6
answers
2k
views
$dU=dQ$ and $dU=TdS$, but $dQ$ not always equal to $TdS$? Why?
$$ dU = dQ+dW $$ $$ dU=TdS-pdV $$ The equations above are always true for a thermodynamic state of a certain system. Now let's say that we have a situation where $dW=0$, this tells us that $$ dU=dQ $$ ...
- 283
1
vote
2
answers
500
views
Entropy irreversibilities
How can we say that a system is reversible or irreversible if not stated?
I encountered a book example wherein a piston cylinder device encounters an isobaric process and experiences a transfer of ...
- 99
1
vote
0
answers
142
views
Questions regarding reversible and irreversible machines
I was going through Feynman's argument of reversible and irreversible machines regarding gravitational potential energy. The lecture is right here. I have understood what he is trying to claim, but ...
- 972