Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange
Join us in building a kind, collaborative learning community via our updated Code of Conduct.

A important extensive property of all systems in thermodynamics, statistical mechanics, and information theory, quantifying their disorder (randomness), i.e., our lack of information about them. It characterizes the degree to which the energy of the system is *not* available to do useful work.

0
votes
0answers
6 views

Lower bound on quantum relative entropy

In my research this summer, I have become interested in lower bounds on the standard "Umegaki quantum relative entropy". For two non-negative matrices $X$ and $Y$, the Umegaki quantum relative ...
0
votes
0answers
12 views

Example calculation of increase in accessible states upon reimposing constraints in an isolated system?

Can you show me some example calculations of where the accessible states of a system increase upon reimposing the constraints of an isolated system (like moving the piston in a cylinder back to its ...
-1
votes
0answers
24 views

Do pure gases mix together quicker than already mixed gases?

Imagine a box split into two compartments by a gas-impermeable barrier. In one half is, say, pure oxygen, and in the other is pure, say, nitrogen. You remove the barrier, and the gases mix, eventually ...
1
vote
0answers
31 views

Quasi Static Reversibility Theorem

As far as I know, the definition of a reversible process is simply "a process that can be reversed". Meaning, that for an isolated global system containing the subsystem in question, its thermodynamic ...
6
votes
2answers
105 views

Confusion about entropy when applied to the whole universe. What are the macrostates?

I'm really confused about the concept of entropy when applied to the whole universe. The often hear that the universe started with very low entropy and as the entropy increases the universe will ...
14
votes
1answer
556 views

If entropy is a measure of disorder, how come mixing water and oil finishes in a well ordered, separate state? [duplicate]

By the second law of thermodynamics, entropy tends to increase when the system is let on itself. And if entropy is a measure of disorder, how come mixing oil in water and letting the system reach ...
1
vote
2answers
83 views

Do liquids have a higher entropy before or after being mixed together?

Suppose I mix oil and water by stirring the liquid, then which state has the higher entropy, the mixed or the unmixed state? Is this similar to: When mixing coffee and milk, which state has the ...
1
vote
1answer
29 views

Is there any method to estimate the entropy generation inside the metal wall connecting two heat reservoirs?

Hi everyone! I have to split the entropy generation of this system into the species according to the individual component. As far as I know, the entropy generation can only obtain for a whole system ...
0
votes
2answers
34 views

Isentropic process and compression

Suppose we compress a gas from $(p,t)$ to $(P',T')$ reversibly & adiabatically (isentropically). If we perform non-isentropic irreversible compression from $(p,t)$ to $(P',T)$, we can say with ...
2
votes
1answer
59 views

Entropy of natural networks [duplicate]

How does one define the entropy of a natural network (say for example, a river network, or a morphological skeletal network of a lake in the figure below) ? For example, the following report suggests ...
0
votes
0answers
30 views

Entropy estimation in Guth (1981)

I am trying to understand step-by-step Guth's famous paper "Inflationary universe: A possible solution to the horizon and flatness problems" I am stuck at his discussion of the flatness problem. On ...
0
votes
1answer
51 views

Is entropy lower at zero temperature or the Planck temperature?

I have already asked a question about entropy, Entropy and temperature, but I think this question is more pertinent and very different. It is said that object with very low entropy have a lot of ...
0
votes
0answers
36 views

Entropy and temperature

I have been studying the concept of entropy and I have seen many examples involving the local decrease of entropy by cooling an object. Some definitions of entropy state that low entropy is when there ...
0
votes
0answers
23 views

Entanglement entropy calculation

I have been trying to understand this paper: Susskind. “Black Hole Entropy in Canonical Quantum Gravity and Superstring Theory.” [1402.1128] Long Short-Term Memory Based Recurrent Neural Network ...
0
votes
2answers
68 views

A paradox involving heat exchange between two heat sources

If you suppose to put in contact two ideal heat sources at the temperatures $T_{1}$ and $T_2$ with $T_{1}<T_{2}$ you obtain a strange thermodynamics process. If you consider just one of the two ...
0
votes
1answer
54 views

Does violation of second law of thermodynamics become violation of law of conservation of Energy? [closed]

Suppose if we were to violate the second law of thermodynamics and produce work entirely of heat from a single temperature. We can then heat a source of higher temperature with aforementioned work. We ...
2
votes
2answers
77 views

Could a Carnot engine linked to a Carnot “refrigerator” create a perpetual heat flow between two reservoirs?

Here is a diagram of the system in question (adapted from the diagram on this page): All of the work produced by the Carnot engine is used to drive the Carnot refrigerator, which is simply a Carnot ...
0
votes
3answers
101 views

2nd law of thermodynamics and gravity

If I have a container with gas according to my understanding of 2nd law of thermodynamics molecules/particles will not be at one side of the container but if the container gets energy from outside ...
0
votes
0answers
44 views

Measuring the entropy of mixing ideal gases

Suppose I have two compartments of volume V separated by a barrier. Each one has an ideal gas, pure, of N molecules, and with equal pressure and temperature. However, I don't know whether both gases ...
2
votes
0answers
54 views

How does the virial expansion converging, mean that there is no phase transition?

I have a question regarding how the virial expansion relates to phase transition. I watch the lecture https://www.coursera.org/learn/statistical-mechanics/lecture/1a5Di/tutorial-3-algorithms-exact-...
2
votes
1answer
49 views

Is partition function algorithm-dependent or configuration-dependent?

I am reading this resource to learn statistical mechanics: http://blancopeck.net/Statistics.pdf I am trying to learn about the partition function, which as I understand it, is equal to the number of ...
2
votes
1answer
64 views

Can you reverse the arrow of time?

Has there been any attempt to reverse the arrow of time?
2
votes
1answer
46 views

If heated molecules are more disordered, why doesnt it happen spontaneously?

currently, the way I understand entropy is disorder and that it always increases. I therefore have difficulty to understand why don't object heat spontaneously(i.e take in energy from their ...
0
votes
0answers
30 views

Are attempts to extract useful work from spontaneous decreases in entropy an example of Maxwell's demon?

Something I see often in forums discussing future energy sources is perpetual motion of the second kind. Rather than outright denial of the second law, however, they say the fluctuation theorem shows ...
2
votes
3answers
82 views

About Entropy Definition

I quote the coming lines from Igneous & Metamorphic Petrology by Myron G. Best (2003): One statement of the second law of thermodynamics is that spontaneous natural processes tend to even out ...
1
vote
2answers
78 views

Is Entropy Backwards?

Is it weird that everything with a gradient goes from high to low except for entropy? High pressures try to fill in low pressures, high temp goes to low temp, osmosis happens from high to low, etc. ...
0
votes
0answers
34 views

Does Verlinde's entropic gravity relate Hawing radiation to bodies other than black holes?

To the best of my understanding this is the essence of the point he's trying to establish, am I right in thinking this?
0
votes
1answer
54 views

Calculation of heat generated due to friction for air flowing through a pipe

I am currently attempting to calculate the heat transfer when compressed air is flowing isothermally through a pipe with frictional losses. I realise this might seem like an odd question, but I am ...
2
votes
1answer
108 views

Canonical ensemble near absolute zero

In the canonical ensemble for an ideal gas of $N$ bosons, the partition function for $T\to 0$ scales like $$Z\sim e^{-\beta\epsilon_0N},$$ when $\epsilon_0$ is the lowest (non-degenerate) single ...
5
votes
1answer
85 views

Entropy has units of energy-per-temperature; what is the impled relation between energy and temperature?

Entropy has units of energy-per-temperature, e.g. $X$ joules per Kelvin. Can this be reduced to a simple English sentence that describes the relationship between those $X$ joules and 1 Kelvin? For ...
0
votes
1answer
30 views

Where does energy in osmosis come from?

So I get that work is done when a net force converts potential to heat or kinetic. But I also understand that osmosis is driven purely by entropic processes. There is no net force, only a statistical ...
1
vote
1answer
85 views

If a star forms, entropy decreases… but doesn't this require some form of energy?

A cloud of matter has high entropy. In order to form a star out of matter, the entropy must decrease. For this, energy is necessary. Where does this energy come from?
1
vote
2answers
47 views

Why is entropy generation zero at infinitesimal temperature gradient?

First question: Is the question I asked valid in the first place? Is it really true? Second question: If so, is it because the exchanged heat between the bodies between which the temperature gradient ...
0
votes
1answer
37 views

In what ways can entropy of the universe increase?

So far, I have been able to come across two scenarios in which entropy of the universe increases. First, when heat flows at a finite temperature gradient and second, during expansion of air particles ...
0
votes
1answer
44 views

What will the universe be made of at the heat death?

Explain it to me like I'm a five year old. It's the far distant future and the universe has finally come to its heat death. At this point, what will be left of the universe? Will there perhaps only ...
0
votes
0answers
24 views

Entropy production during leptogenesis

Do the out of equilibrium decays of right-handed neutrinos in standard leptogenesis scenarios lead to a net entropy production? Does this entropy production lead to observable effects (like reheating)?...
2
votes
0answers
41 views

Entropy of the ideal gas - How to derive the $S(U,V,N)?$

I'd like to derive the $S(U,V,N)$ function. In the lecture, we were using the $S=k_b \log(\Omega)$, some combinatorics, approximation, $6N$ dimensional spheres, etc. But I'd like to avoid that if it's ...
0
votes
0answers
50 views

Thermodynamics: Calculate heat flow

I was given the following scheme of a power plant: $ {\def\place#1#2#3{\smash{\rlap{\hskip{#1px}\raise{#2px}{#3}}}}} % \place{300}{290}{\begin{array}{c} 60 \, \mathrm{bar} \\ 575\sideset{^{\circ}}{}{\...
2
votes
0answers
54 views

Absolute entropy at 0 K and residual entropy

The third law of thermodynamics states that the absolute entropy of a pure crystalline substance is $0$ at $0\,\mathrm{K}$. In the analysis of chemical reactions this absolute scale is sued to ...
0
votes
1answer
67 views

Calculating entropy for the surroundings the logical way doesn't work

EDIT: I was missing the entropy change due to temperature change and now everything makes sense Suppose I have $n$ mol of an ideal gas in a chamber with a piston with volume $V$ at pressure $P_{1}$ ...
0
votes
1answer
23 views

Entropy and heat death

If elements or particles(can a single particle have temperature) ... have different thermal capacities how can we determine the heath death and why is it identical for everything ?
4
votes
0answers
73 views

Von Neumann entropy in the algebraic approach

In the algebraic approach to QM a quantum system has associated to it one $\ast$ algebra $\mathfrak{A}$ generated by its observables. A state is a positive, normalized linear functional $\omega : \...
0
votes
2answers
84 views

Can we have situations where thermodynamic extensivity is violated?

In thermodynamics, the internal energy $U$, the number of particles $N$, the entropy $S$, etc. are extensive properties. Can there be situations where the extensivity is violated?
0
votes
1answer
54 views

Entropy of water drop

The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time. However, if the drop of water falls into water, splashes decrease and disappear over ...
3
votes
0answers
28 views

Holographic dualities and strong subbadditivity of entanglement entropy

Recent analysis of inequalities satisfied by entanglement entropy in AdS bulk duals have led to establishing an equivalence between Strong Subadditivity and the Null Energy Condition (NEC) How hard ...
2
votes
0answers
34 views

What sense is there in entropy arguments when the system can't be known to be ergodic?

What sense does "entropy" make in non-equilibrium dynamics? What is its definition? How is the "entropy of the early universe" calculated, for example? And how can the "entropy of the universe" be ...
0
votes
1answer
37 views

What temperature should be taken into consideration when calculating the entropy change?

Introduction In this question I want to know when calculating the entropy change where we take the temperature of the system or the reservoir's and if my thought process is sound. Clausius Theorem ...
7
votes
1answer
360 views

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 ...
2
votes
2answers
37 views

Can the ideal gas expand adiabatically and irreversely?

Suppose that the ideal gas is expanding adiabatically from the state $(P_1, V_1, T_1)$ to the state $(P_2, V_2, T_2)$ I think this process can be allowed to happen reversibly or irreversibly, but ...
0
votes
1answer
74 views

Entropy change in a reversible adiabatic expansion of ideal gas

Below is P-V curves of 1 mole of ideal gase for temperature 700K, 500K and 300K each. Now I would like to calculate entropy change of the system along the path from (1) to (3), which is adiabatic ...