0
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1answer
26 views

Isentropic process and reversibility

I know that every adiabatic reversible process is an isentropic process. Can a process be isentropic but still not reversible adiabatic? Please provide me some examples.
0
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0answers
14 views

Unmixing of gases: What is the relevant temperature for my Entropy?

This answer to a question about unmixing gases states: However, let us now assume we have to hand a source of mechanical work, and a large heat reservoir at temperature $T$. I'll assume that ...
0
votes
2answers
33 views

For change in entropy dS = dq/T, is T the temperature of system or surrounding or both?

For change in entropy dS = dqrev/T, is T the temperature of system or surrounding or both? I am confused about Thot, Tcold, Tsys and Tsurr. If qrev, are we talking about the reversible cycle such as ...
2
votes
2answers
108 views

Does entropy have a physical meaning?

Entropy is incredibly useful as a mathematical tool. But what does it actually mean? I understand that the Boltzmann entropy is defined by: $$S=k\ln{\Omega}$$ With $\Omega$ being the multiplicity ...
0
votes
0answers
15 views

Entropy changes with the reversible and irreversible expansion of an ideal gas [closed]

a) What is the entropy change for 1.00 mol of H2(g) that has undergone a reversible expansion from 0.01m^3 at 100K to 0.100m^3 at 600K. For hydrogen, Cp = 29.066-0.836x10^-3T+20.17x10^-7T^2 in ...
1
vote
2answers
34 views

Does the relation between entropy and temperature depend on the ensemble?

If we change the temperature of a given system, there will be a relation between its entropy and temperature S(T). Is S(T) the same in a canonical ensemble and a grand canonical ensemble? If not, is ...
3
votes
3answers
79 views

Definition of Entropy in thermodynamics

In most textbooks, the definition of entropy in reversible processes on a system $S$ is given simply as $$d S=\delta Q/T.$$ It seems to me this definition is insufficient since it does not specify ...
3
votes
2answers
103 views

“Violation” of the Second Law

I can't reconcile some facts about entropy and irreversibility. This depresses me, because I feel I can't quite grasp the importance of entropy. I will illustrate my problems with an example given by ...
1
vote
1answer
32 views

Can you choose the variables of a state function?

I'm confused. I was first introduced to entropy as a state function of internal energy and volume $$S(U,V) \Rightarrow dS = C_v\frac{\mathrm{d}T}{T} - p\frac{\mathrm{d}V}{T} $$ wich is the ...
0
votes
1answer
58 views

Helmholtz free energy from a relation for entropy

The Legendre transformation defines the helmholtz free energy (at least according to my lectures) as: $F(T,V,N)=E-TS$ It also says to start with $E(S,V,N)$ and $T=\frac{\partial{E}}{\partial{S}}$ ...
3
votes
4answers
119 views

Difference between heat capacity and entropy?

Heat capacity $C$ of an object is the proportionality constant between the heat $Q$ that the object absorbs or loses & the resulting temperature change $\delta T$ of the object. Entropy change is ...
3
votes
1answer
68 views

Definition of entropy in nonequilibrium states

Thermodynamical definition of entropy $$S(p)=-\int p\ln p~dx$$ is defined only on equilibrium system. But why can't we use it for non-equilibrium system? Is there a well-accepted definition for it?
5
votes
2answers
54 views

Thermodynamics of scattering theory

I have a couple of conceptual questions regarding the thermodynamics of scattering. Any partial answer or argument will be appreciated. For the sake of discussion, consider the scattering of ...
1
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3answers
83 views

Is there a minimum energy content of information, other than 0 Joules?

Lets say I want to send the bit string 010110 to someone. Is there a theoretical lower bound on the energy needed to do this?
2
votes
2answers
151 views

Is the second law of Thermodynamics an immense tautology?

Let's imagine for a second a system that is changing constantly from one microstate to another one. It could be a given volume of a gas with its atoms moving and bouncing around, or a deck of cards ...
3
votes
3answers
267 views

Axioms behind entropy!

The concept of entropy is very ubiquitous, we learn about its uses starting from Information Theory (Shannon entropy) up to its basic definition in statistical mechanics in terms of number of ...
1
vote
1answer
108 views

Gravity and the Second Law of Thermodynamics [duplicate]

I was wondering about the hypothetical - and apparently improbable - heat death of the Universe when I stumbled upon this seeming contradiction. A certain volume of space with a uniform distribution ...
2
votes
2answers
122 views

Who invented the perfume bottle thought experiment?

A common thought experiment used to explain the second law of thermodynamics, the "arrow of time", etc. is perfume escaping from an opened perfume bottle; the perfume is likely to diffuse into the ...
1
vote
1answer
99 views

Thermodynamics for Dummies: Entropy and temperature

I do not study physics and I have never had a course in thermodynamics. I have no idea what it is about, but I am currently taking a course where we had something about entropy. Would be great if ...
4
votes
3answers
88 views

Is Fourier's law of conduction a consequence of the second principle?

In classical thermodynamics courses, entropy is often motivated by the need to justify that heat flows from high temperatures zones to lower temperatures zones: this is seen as a consequence of ...
6
votes
4answers
98 views

Entropy and dark matter structure

Inspired by this question. I believe that the usual explanation that preserves the second law of thermodynamics as an astrophysical gas cloud collapses under gravity is that the gas must heat and ...
3
votes
3answers
103 views

Are galaxies, stars, planets, and ultimately life in violation of the second law of thermodynamics? [duplicate]

How can we think about entropy in these situations? To my knowledge all of these structures are born out of gravitational interaction. However, it would seem that the formation of these more organized ...
6
votes
9answers
1k views

What is entropy really?

On this site, change in entropy is defined as the amount of energy dispersed divided by the absolute temperature. But I want to know: What is the definition of entropy? Here, entropy is defined as ...
0
votes
2answers
63 views

What is entropy of the universe? [duplicate]

What is entropy of the universe? What is the change in entropy of our universe? Is this change increases or decreases? If the entropy of universe keeps on increasing then what are the consequences? Is ...
2
votes
2answers
102 views

How can heat turn into light

I am confused about how hot surfaces can radiate light to their surroundings. When I shine a light on a surface the light turns to heat spontaneously, and when I leave that hot surface it radiates ...
2
votes
0answers
50 views

Is the second law of thermodynamics a real law? [duplicate]

Everytime I ask people why the second law of thermodynamics is true, they say because the probability of entropy increasing is very large. This for some reason doesn't seem right for me. Just because ...
2
votes
3answers
158 views

Why is Entropy's Definition Useful?

I have somewhat of an understanding for other physical quantities, but as far as entropy goes I only know it to be "disorder". Why is the change in entropy formula an appropriate/useful definition, ...
1
vote
0answers
50 views

Confusion on entropy in the universe [closed]

I was researching about the heat-death of the universe, and I was wondering if my understanding of it so far is factual to the theory? However, the 3rd Law of Thermodynamics prevents the universe’s ...
4
votes
4answers
388 views

Mathematical proof of the Second Law of Thermodynamics [duplicate]

Is there some book or paper that formalizes statistical mechanics, like some people have done with relativity, and proves the second law of thermodynamics from more foundational axioms?
0
votes
3answers
83 views

Does the entropy of an adiabatically isolated system stays the same after we decrease/increase the pressure?

Even if the system is isolated and there is no heat exchange with surroundings, shouldn't the decrease/increase of pressure result in increase/decrease of entropy? Does this property of an ...
4
votes
2answers
198 views

Is this theory about Universe and information true?

I recently saw this video about information and randomness. At some point, it states that a completely predictable universe would infringe the second law of thermodynamics, because it would imply that ...
4
votes
3answers
112 views

Problems with units of entropy in statistical thermodynamics

The statistical thermodynamics definition of entropy: $S = kN \ln (W)$ troubles me a lot with the problem of dimenstions. where $S$ is entropy; $k$, the Boltzmann constant; $N$ the number of particles ...
4
votes
3answers
200 views

Existence of negative temperatures and the definition of entropy

How negative temperatures can be possible has been treated on StackExchange before (several times in fact), but in light of some recent academic discussion, most of these answers seem to be possibly ...
4
votes
3answers
195 views

Problem about entropy

Combining the first and second law of thermodynamics we can get the following equation $$TdS=dU-P_{ext}dV$$ First question: Is this equation applicable for irreversible processes such that that ...
2
votes
1answer
100 views

Relativity of simultaneity and the second law of thermodynamics? [closed]

Has the connection been noted between these two? I have been studying special relativity and in learning Minkowski diagrams I have noticed that as v approaches c, the relativity of simultaneity is so ...
4
votes
4answers
169 views

Question on entropy

All of my textbooks mention, that entropy-change of all spontaneous physical, and chemical processes is positive, and that such processes need another condition to fulfill- decrease in the net ...
0
votes
3answers
186 views

Why can the entropy of an isolated system increase?

From the second law of thermodynamics: The second law of thermodynamics states that the entropy of an isolated system never decreases, because isolated systems always evolve toward ...
1
vote
0answers
22 views

Thermodynamics of binary symmetric channels

I am reading this very interesting paper: http://m.iopscience.iop.org/1751-8121/41/40/402002/pdf/1751-8121_41_40_402002.pdf about thermodynamics of channels in information theory. More generally, ...
2
votes
3answers
155 views

How does the evolution of a solar system not break the second law of thermodynamics?

Please forgive: I am a layman when it comes to physics and cosmology, and have tried finding an answer to this that I can understand, with no luck. As I understand it, the solar system evolved from a ...
2
votes
1answer
83 views

Entropy is constant. How to express this equation in terms of pressure and density?

In hydrodynamics of an ideal, non-compressive flow we use 5 variables: pressure $p$, density $\rho$ and velocity field $\mathbf{v}$. So we need 5 equations. Landau's "Hydrodynamics" states that the ...
3
votes
1answer
101 views

Explicit form of the entropy production in hydrodynamics

I'm trying to understand how hydrodynamics arise from a precise, mathematical formulation of thermodynamics, learning mostly from Landau's "Hydrodynamics". So Landau starts from formulating the ...
2
votes
0answers
98 views

Is there a relation between (non-) existence of magnetic monopoles and thermodynamics?

This question follows on previous work on connections between (other) areas of physics and thermodynamics as in here, here and even here. P. Dirac (an electrical engineer initially) was one of the ...
1
vote
2answers
227 views

Is quantum uncertainty principle related to thermodynamics?

Would like to ask a question, but first i would like to say Hello Everybody in a way that plays the system, since some geniouses decided that one should not be able to say hello in a question. The ...
10
votes
1answer
198 views

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 ...
0
votes
2answers
84 views

The entropy of the universe in an irreversible cycle [closed]

Suppose we have an ideal gas performing an irreversible cycle composed by: an isothermal transformation at $T_{1}$; an isobaric transformation at $P_{A}$; an isothermal transformation at $T_{2}$; an ...
30
votes
7answers
3k views

Homemade salad dressing separates into layers after it sits for a while. Why doesn't this violate the 2nd law of thermodynamics?

The oil, vinegar and other liquids in homemade salad dressing separate into layers after sitting for a while, making the mixture become more organized as time evolves. Why doesn't this violate the ...
2
votes
2answers
178 views

Entropy $dQ=TdS$ and Work $dW = -pdV$ conditions?

What are the conditions in order for the equations: Entropy $dQ = TdS$ and Work $dW = -p dV$ to work? I think for $dQ = T dS$, it must be a reversible process? But for $dW = -p dV$, shouldn't it ...
18
votes
5answers
2k views

Where does deleted information go?

I've heard that, in classical and quantum mechanics, the law of conservation of information holds. I always wonder where my deleted files and folders have gone on my computer. It must be somewhere I ...
0
votes
2answers
107 views

Information or Matter or Energy

Which one is the most fundamental of the universe? What it is made of? Physicists are searching for unique and fundamental form. The question is , information is more fundamental than energy ? ...
0
votes
1answer
73 views

consequences of universe in which second law of thermodynamics does not hold [closed]

What would happen if the second law of thermodynamics was not there for governing in every day processes. Can a universe exist and evolve if the second law of thermodynamics does not exist in first ...