A important property of all systems in thermodynamics and statistical mechanics. Entropy characterizes the degree to which the energy of the system is *not* available to do useful work

learn more… | top users | synonyms

1
vote
3answers
125 views

Entropy change in an irreversible process between 2 equilibrium state

Calculating entropy change in an irreversible process between 2 states requires computing the change in entropy for any reversible process between the 2 same states, but why? If someone could provide ...
0
votes
4answers
74 views

If heat can't be transformed into other forms of entropy, why do hot things radiate electromagnetic waves?

The laws of entropy says entropy can only increase. On the other hand, if I take a hot object, it will naturally convert its heat into EM radiation. How is this possible? Does EM radiation count as ...
21
votes
4answers
720 views

Intuitive understanding of the entropy equation

In thermodynamics, entropy is defined as $ d S = \dfrac{\delta q_{\rm }}{T}$. This definition guarantees that heat will transfer from hot to cold, which is the second law of thermodynamics. But, why ...
25
votes
8answers
2k views

How is $\frac{dQ}{T}$ measure of randomness of system?

I am studying entropy and its hard for me to catch up what exactly is entropy. Many articles and books write that entropy is the measure of randomness or disorder of the system. They say when a gas ...
3
votes
5answers
573 views

Integrating factor $1/T$ in 2nd Law of Thermodynamics

How would you prove that $1/T$ is the most suitable integrating factor to transform $\delta Q$ to an exact differential in the second law of thermodynamics: $$dS = \frac{\delta Q}{T}$$ Where $dS$ is ...
10
votes
8answers
1k views

Why does heat added to a system at a lower temperature cause higher entropy increase?

Entropy is defined in my book as $\Delta\ S = \frac{Q}{T}$. To derive the formula it says that entropy should be directly proportional to the heat energy as with more energy the particles would be ...
2
votes
2answers
338 views

The definition of entropy

As history of thermodynamics say, it was a mystery that what is the required condition for a given energy conversion to take place? Like there are two possible events each conserving energy but only ...
3
votes
5answers
1k views

How does the entropy of an isolated system increase?

The change of entropy is defined $$\Delta S = \int \frac{dQ_\mathrm{rev}}{T}.$$ If a system is isolated the heat transfer between the system and the surroundings is zero ($dQ = 0$), thus $\Delta S = ...
1
vote
2answers
955 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 ...
0
votes
2answers
71 views

Entropy and the $2^{nd}$ law of thermodynamics

I have just been introduced to the word "entropy" and as it is my understanding that it is a measure of the randomness and chaos of particles in as system. My textbook list the 2nd law of ...
0
votes
2answers
98 views

Second law of thermodynamics (in terms of entropy)

Is the second law of thermodynamics (in terms of entropy) for closed systems or isolated systems? I thought it must be valid for isolated systems, such as the Universe. But the book Fundamentals of ...
1
vote
6answers
254 views

Entropy Change in an irreversible process

I have just started learning thermodynamics and the concept of entropy confuses me. Suppose I have a gas in a cylindrical container fitted with a piston. I take it through an adiabatic irreversible ...
5
votes
5answers
351 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 ...
0
votes
3answers
200 views

Dimensionless entropy interpretation

Measuring temperature in joules instead in the artificial units of Kelvin would render entropy as a dimensionless quantity. This is quite appealing since entropy has always been quite a misterious ...
61
votes
1answer
4k views

Where is the flaw in this machine that decreases the entropy of a closed system?

I was thinking about a completely unrelated problem (Quantum Field Theory Peskin & Schroeder kind of unrelated!) when the diagram below sprang into my mind for no apparent reason. After some ...
15
votes
3answers
1k views

Why don't photons split up into multiple lower energy versions of themselves?

A photon could spontaneously split up into two or more versions of itself and all the conservation laws I'm aware of would not be violated by this process. (I think.) I've given this some thought, and ...
2
votes
2answers
1k views

Physics-based derivation of the formula for entropy

I am looking for a derivation of the formula $$S~=~-\Sigma_ip_i \log (p_i).$$ for entropy, from first principles. I only wish to assume the laws of physics, and without involving concepts in ...
1
vote
1answer
61 views

Why is the entropy of most systems not infinite?

We can define a microstates as follows: Definition 1: A complete specification of the six coordinates of each molecule of a system, within the limits of the dimensions of the cell in which its ...
0
votes
0answers
32 views

What is the Black Hole Information Paradox?

What is the Black Hole Information Paradox? I read here, when something falls on black hole its physical information is lost and it's physical state is dissolved. But didn't the Hawking say that the ...
3
votes
2answers
118 views

Entropy / Structure Relations

I want to check on the validity of the following objective definition of order. Is it correct? Is there a more rigorous statement of this concept? The further a system is from its maximum ...
0
votes
3answers
79 views

What is the relationship between entropy and work? [closed]

Can someone explain the relationship between entropy and work? I've been reading my textbook and looking online but I feel like I'm missing something. Can someone explain it in layman's terms :)
1
vote
2answers
204 views

Is entropy a meaningful concept on a quantum level?

My naive assumptions, as I really am at a pretty basic stage in QM, are as follows: Classically, entropy gives us a practical measure of the direction of time, as opposed to our physical laws which, ...
1
vote
0answers
54 views

The black hole paradox

I recently read in the news that Stephen Hawking claims to have solved the Black Hole Information paradox. I researched a bit about the paradox and the research that Stephen Hawking did to solve it. ...
4
votes
1answer
108 views
+50

What causes a eutectic point?

What causes the melting point depression known as a eutectic point? The temperature depression of a eutectic point can be calculated from the enthaplies and entropies of fusion of the two ...
1
vote
1answer
38 views

Entropy reversal in magnets

Entropy is an irreversible phenomenon without any energy supplied to reverse it. I was reading about paramagnetic substances and how dipoles align inside them on application of magnetic field. My ...
6
votes
0answers
189 views

Does the radius of the Universe correspond to its total entropy?

I heard a claim that due to holographic principle, the surface area of the cosmic horizon corresponds to the universe's total entropy. As such the initial state had zero surface area and later ...
1
vote
4answers
120 views

Really how does the entropy of the universe increase?

Universe means the system along with its surroundings. I have always got this statement while studying the second law; be it a thermodynamics book(Sears, Salinger) , physical cihemistry book(Atkins, ...
2
votes
2answers
44 views

Multiplicity vs Partition function

I'm a little confused between all the different notations for the multiplicity and partition function. They're not the same thing, are they? I know that entropy can be expressed as $ S = k \ln\Omega ...
0
votes
0answers
12 views

Luminosity and entropy of a relativistic shell

I am looking to understand more about gamma ray bursts. The review I am reading through describes in equations (111), (112) the luminosity of a relativistic plasma shell, in an inertial frame at rest ...
3
votes
1answer
197 views

H-theorem and Boltzmann equation applied to Boltzmann distribution

Using the Boltzmann equation: $$ \frac{dH}{dt} = \int_0^{\infty} dr \int_0^{\infty} ds W(r,s)[p_r - p_s][\ln{p_r} - \ln{p_s}],$$ and assuming $p_r = e^{-\beta r}$, the equation looks like $$ ...
3
votes
3answers
114 views

Entropy of loops in the PV plane

The change in entropy of the Carnot and reversible cycles is said to be 0. Several other loops are supposed to have a non-negative change in entropy. This presents 2 problems which I cannot ...
1
vote
1answer
42 views

Reversible cycle approximated by Carnot cycles

My textbook, W.E. Gettys, F.J. Keller, M.J. Skove, Physics 1, gives the definition of a reversible transformation as a transformation that can be inverted by effectuating only infinitesimal changes in ...
3
votes
1answer
134 views

Simpler derivation of sarkur-tetrode equation

Is there a reason the following derivation for the Sackur-Tetrode equation is not common? I am teaching a lower undergraduate level class and would like to derive it with simpler terms of only using ...
3
votes
2answers
137 views

Is entropy absolute (as in absolute temperature)?

Following this question on the Entropy at the Big Bang where I asked: Since Entropy always increases (in general); its expected that the entropy at the beginning of the universe should be the ...
0
votes
0answers
18 views

Is lost work always positive? How to approve?

I am dealing with a question asking for comment on the sign of lost work. The case is to consider an irreversible process and a reversible process which share the same starting and ending state. Is ...
3
votes
2answers
66 views

Second Law of Thermodynamics and heating a blackbody with another blackbody

Given a large blackbody with surface area $A_1$ and temperature $T_1$, let's assume I can use some mirror and lens system to capture all the emitted radiation and transfer this energy to a smaller ...
15
votes
1answer
1k views

Motivation for the use of Tsallis entropy

Every now and again I hear something about Tsallis entropy, $$ S_q(\{p_i\}) = \frac{1}{q-1}\left( 1- \sum_i p_i^q \right), \tag{1} $$ and I decided to finally get around to investigating it. I haven't ...
2
votes
1answer
660 views

Difficulties with understanding total entropy change and unavailabillty

Of course, I know the fact that the entropy of an isolated system never decreases. Neverthless what makes me confused about the entropy(or change of entropy) of an isolated system is the explanation ...
-1
votes
2answers
144 views

Derive the Sackur-Tetrode equation

How do you derive the Sackur-Tetrode equation? I know that you must start off with the multiplicity of a mono-atomic ideal gas: ...
2
votes
0answers
26 views

Black hole entropy versus entropy of normal matter

It has been established that the entropy of a black hole is equal to: $$ \frac{1}{4} \frac{c^3 A}{ G \hbar} k$$ Which if one substitutes for A the surface area of the event horizon: ...
0
votes
1answer
44 views

Is it true that all processes where entropy increases are permitted by the second law, if the system is isolated?

It is possible to deduce that in a thermodynamic process for an isolated system $\mathrm{d}S$ has to be greater than zero, from this it follows trivially that $ \Delta S > 0$. It is usually said ...
0
votes
1answer
16 views

How does entropy ensure that isolated thermal processes are 100% irreversible?

How can anyone prove that molecules in figure C will never return to their original positions in figure A? It will be more believable to say that the chance is very slim.
15
votes
1answer
396 views

How is the logarithmic correction to the entropy of a non extremal black hole derived?

I`ve just read, that for non extremal black holes, there exists a logarithmic (and other) correction(s) to the well known term proportional to the area of the horizon such that $S = \frac{A}{4G} + K ...
5
votes
1answer
300 views

Is this derivation of Black Hole entropy viable?

This question is motivated by this one. Suppose $l$ is the minimum measurable unit of length. What is entropy of a spinless particle contained in this interval? We know that entropy of a two-level ...
0
votes
3answers
171 views

Mechanism of Hawking's radiation and entropy of the black hole

During Hawking's radiation, a virtual particle with negative energy and mass (from pair of particle and antiparticle) fall into black hole and its real partner having positive energy escape from ...
1
vote
1answer
125 views

Entropy of Black Hole

What is the relation between the entropy of rotating and non rotating Black hole? Which one has greater entropy?
3
votes
1answer
136 views

Exploding planets and entropy

Say we have a planet and we blow it up to tiny pieces that gets spread out in a cloud of debris around the planets original location. This cloud of debris is analogue to a cloud of water wapor in ...
2
votes
3answers
9k views

Entropy Change During Reversible Processes

I'm confused about the Second Law of Thermodynamics. The Second Law of Thermodynamics prohibits a decrease in the entropy of a closed system and states that the entropy is unchanged during a ...
1
vote
0answers
38 views

Expression of heat by the Brownian motion

folks. I was reading a paper from PRE and I'm not sure what's going on about the following equation. So for the system composed of two heat baths governed by Brownian motion, the entropy change of the ...
6
votes
3answers
5k views

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 ...