Entropy Definition and 1000 Threads

Homework Statement http://postimage.org/image/9artvc1h5/ see attached Homework Equations ΔS=Q/T The Attempt at a Solution The real issue I'm having is how to go about solving this, I think I'm going to need to use kinematics to find the time the gold is exposed to the air...

I am reading Cycles of Time by Penrose, page 71-72. Could someone explain if the universe started out with at a state of extraordinarily tiny entropy or a state of maximum entropy and what proof or theories do we have to justify this choice. I find the explanation in the book confusing...

What are the formulas for entropy and internal energy in Fermi-Dirac statistics, and how do I derive them?

Homework Statement In a previous problem I had to find the entropy of a black hole where I ended with this: S_{BH}=\frac{8 \pi^2 G M^2 k}{h c} Now I am to find the temp, given the energy of a black hole is mc2. Homework Equations T=(\frac{\partial S}{\partial u})^{-1} The...

Homework Statement The entropy of an ideal paramagnet is given by S=S_{0}+CE^{2}, where E is the energy (which can be positive or negative) and C is a positive constant. Determine the equation for E as a function of T and sketch your result. Homework Equations [tex] \frac{1}{T}=\frac{\delta...

I don't want to argue about whether the notion of "wave function collapse" is a good way of understanding quantum mechanics, or not. For the purposes of this discussion, let's just adopt uncritically the naive approach to quantum mechanics, that: Between measurements, the system evolves...

A formula for entropy: dS=dQ/dT This is a formula that represents the rate of change of heat with respect to temperature. Q=mcdT This is another formula that states how the temperature changes as heat is added. from this can we say that entropy is just specific heat capacity * Mass...

So, until now I know: (DV/DS)p=(DT/Dp)s=a*T/cp*(rho) (enthalpy) (Dp/DT)v=(DS/DV)t=-a/k (helmoltz) (DS/Dp)t=-(DV/DT)p=-Va (gibbs) a=expansion coefficient k=isothermal compression coefficent cp=heat capacity at constante pressure I want to deduce DT/DV at constant entropy=(DT/DV)s. BUT...

I'm having a hard time reconciling two ideas in physics. One is that systems tend towards the maximum amount of disorder, or "entropy always increases". And, when two systems are brought together they are likely to be found at the energy E* which maximizes the number of states of the...

Hello I may well be all wrong about this but I am trying to understand from a microscopic point of view why Entropy is a concave function of internal energy. I found this in the following .pdf: http://physics.technion.ac.il/ckfinder/userfiles/files/avron/thermodynamics_potentials.pdf I...

Hello dbmorpher here, I was looking at some articles on entropy and wondered, could this be used to calculate time? Entropy is known as the arrow of time, figurative I know but could actually be used to measure. If there was a device that calculated the entropy in a set system couldn't it...

Using a simple example: air, why does it naturally form a uniform mixture? Brownian motion wouldn't differentiate between different gases that make up the air.

N.B. My set question is actually almost identical to another posted here https://www.physicsforums.com/showthread.php?t=368672 but my question is not answered there. Homework Statement The temperature inside a refrigerator is 275K. The room containing it has a temperature of 295K. In...

Trying an example from a textbook but I don't understand Legendre transform at all. "construct Legendre transforms of the entropy that are natural functions of (1/T, V, n) and (1/T, V, μ/T)". I don't really understand where to start. An example prior to this exercise just states: A = E - TS =...

I just have this confusion which is completely eating me up. They say entropy of a system is a state property. Then they say that for a completely isolated system, entropy either increases or remains zero depending on the process being irreversible or reversible. So, let's say for an...

Hello I was wondering, with regards to the Tds equation Tds = de + pdv: 1. All of my textbooks state that integrating this equation, although derived for a reversible process, will give the entropy change regardless of the process or whether or not the process is reversible. However, I...

Homework Statement We have a piston in a cylinder containing Helium. The initial states are: P1=150kPa T1= 20°C V1=0.5m3 Following a polytropic process, the final states are: P2=400kPa T2=140°C V2 is unknown. We're also given R=2.0769 kPa.m3.(kg.K)-1 And Cp=5.1926kJ.(kg.K)-1 As...

We know that if we brought a body at temperature T' in contact with a heat reservoir at temperature T (where T' < T) entropy of the universe increases. What if we brought a body at temperature T' in contact with a reservoir at temperature T ( where T' > T)? It is supposed also that the entropy...

Entropy -- can only calculate entropy only at constant temperature? Is that possible to calculate entropy when dq=+100J , temperature change from 271K to 273K ? Ice melt until 273K , not an isolated system. Or I can only calculate entropy only at constant temperature? Thank you

There have been some discussions here as to what type of processes create entropy rather than just move it around. It is established that a gradient of temperature can create entropy. However, the issue moved to partial pressure, and then even away from that. The previous discussion...

"change" in entropy While reading a textbook on introductory thermodynamics , I came across the following- "When a system is in equilibrium, the entropy is maximum and the change in entropy ΔS is zero " And also "We can say that for a spontaneous process, entropy increases till it reaches a...

Hi there, I have to solve this problem: Use the following data to estimate the molarity of a saturated aqueous solution of ##Sr(IO_3)_2## So, I think I should use the Van't Hoff equation in some way, but I don't know how. I also have: ##\Delta_r G=\Delta G^o+RT\ln K## ##K## is the...

Homework Statement 1 kg of water with specific heat (C) of 4180 Joules /kg/degree is given at 0°C. It is taken to 100°C by two methods :- (i) by bringing it in contact with a reservoir at 100°C. (ii) by bringing it in contact with a reservoir at 50°C , and then with another reservoir at...

From theory, we know that Boltzmann entropy for a given distribution, defined through a set of occupancy numbers {ni}, of the macrostate M, is given by: S=k log(Ω{ni}) where omega is the number of microstates for the previously given set of occupancy number, {ni} . Assuming that the system...

Entropy is a measure of energy availiable for work ? "Entropy is a measure of energy availiable for work". Can someone explain this to me? Give some examples that show in what sense it is true. It has to come with a lot of caveats, proviso's etc. because its simply not true on its face. I...

Homework Statement I was asked to prove that (dP/dS)T (subscript T ie, at a constant temperature) equals κPV ("kappa"PV, or, isothermal compressibility x pressure x volume). By using the Maxwell relation -(dS/dP)T = (dT/dV)P I got an answer of -1/(alpha*volume) but cannot find out how to...

How do I go from the entropy of a system, S(U,V,N), to its internal energy, U(S,V,N)? For instance, for an ideal classical gas, we have S=(3/2)N*R*ln(U/N) + N*R(V/N) + N*R*c where R is the Boltzmann constant, N is the particle number, V is the volume and "c" is a constant. How can I...

Hi PF, I would like to implement different random number generators using AVR microcontroller (both PRNG and TRNG). So I would like to get suggestions about different sources of entropy for TRNG and algorithms for PRNG. Also wanted to test the randomness. And What is chaos theory...

What exactly is entropy?

For a system that is completely isolated from its surroundings, basic thermodynamics requires that the quasi-static heat flux dQ and the entropy change dS be related by: dQ = TdS and since the system is isolated...

Given a system of multiple free electrons. Say 2 of the electrons accidentally collide and become joined (opposite spin) by the weak force. So, the positions of those 2 electrons are now correlated. Was the total entropy of the system reduced by those 2 electrons joining? Thank you...

A friend asks me this. If considering the equation: ∫\frac{dQ}{T}, then it is technically feasible to work out some forms of expressions with measurable physical quantities like temperature and specific heat, therefore it is possible to work out a precise value for entropy change. But is there a...

Homework Statement Hello everyone. My problem is as follows: In a spontaneous process where two bodies at different temperatures T_{1} and T_{2}, where T_{1}>T_{2}, are put together until they reach thermal equilibrium. The number of atoms or molecules of the first is N_{1} and N_{2} for the...

I am asking this question because I am trying to understand what entropy is and I just can't seem to get it clear. Now I think the asnwer is 0.5. The pressure of the can is 30. the Atmospheric pressure is around 15. You divide the pressure in the can by the atmospheric pressure and you...

Homework Statement I have the equation Z=1/N!h3N∫∫d3qid3pie-βH(q,p) How can I get the entropy from this equation assuming a classical gas of N identical, noninteracting atoms inside a volume V in equilibrium at T where it has an internal degree of freedom with energies 0 and ε What...

Homework Statement the problem that i was give as homework, is the question "how do we reduce residual entropy experimentally?" Homework Equations the residual entropy occurs when the calculated molar entropy is greater than measured value, thus S bar calc - S bar exp = residual...

Entropy is the measure of ored and disorder. But who tells that what is order and what is disorder? Isnt it a relative or subjective thing? How to define it in general, or it can be definet only for thermodinamic systems?

If 12007 kJ of heat is lost to the surroundings with an ambient temperature of 25 degrees centigrade during a cooling process, and the ambient temperature of the surroundings is unaffected by the heat addition, what is the entropy change of the surroundings? If Δs=∫δQ/T, then Δs=ΔQ/T=12007...

Common extensive quatities such as mass, charge, volume can be defined for general systems. I can imagine that we can measure and define them without any problem in case of any kind of complex system as well. However, I do not know the general definition of the entropy, only the thermodynamic...

Does entropy in a closed system always increase OR remain constant ( in equilibrium ). I have a friend arguing it is ALWAYS increasing. His latest argument was, "if no energy enters or leaves an isolated system, the availability of the remaining energy decreases."

I'm wondering if there's an expression/correction for finding the entropy of a density using histograms of different bin sizes. I know that as the number of bins increases, entropy will also increase (given a sufficient number of data points), but is there an expression relating the two? All I...

I'm a little confused about entropy and it's increase along the arrow of time. My perception of entropy is that it is a measure of order in a system and that high entropy represents dissorder. The final result given sufficient time. From what I have read, the universe has began with low and...

Why is the standard entropy of aqueous ions negative? I thought it could be no less than 0, which represents a perfect crystal at 0 K? Is it negative so that calculations can be performed properly? Or is it because it because ions solutes actually have less entropy than a perfect crystal?

Reading popular books (written by Hawking, Penrose, Greene, Linde, Guth and certainly many more) one finds numerous statements like entropy was low after the big bang ... Weyl-curvature hypothesis ... entropy increases with time ... black holes violate unitarity and therefore entropy or phase...

Greetings, I want to ask you somthing if i understood well this subject. Lets say we have an order 1 binary source. H(a)=-Paa*log(Paa)-Paa*log(Pab) bit/symbol. From what i understand this is the average information of a symbol generated after an "a", like aa or ab. Is it right?

I just heard about entropy from another thread, so I had to go and google it, I lightly skimmed this wiki page...

Assuming a mini-universe with the same laws as our current one. A gas within that universe reaches a state of maximum entropy. Would it remain in that state of maximum entropy once it is reached? Maybe the question does not make much sense. In that case, forgive my ignorance. edit: the...

Entropy of molten lead "freezing" Lead melts at 327.5 C.° The latent heat of melting of lead is 24.1 J/g, and the heat capacity of solid lead is 0.14 J/g °C. You take 100 grams of molten lead at a temperature of 327.5 C° and pour it on the sidewalk. The lead freezes and then comes into thermal...

Homework Statement I am having trouble working out the change in Entropy. The question is as follows: A mass of 1 kg of air is initially at 4.8 bar and 150 degC and it is enclosed in a rigid container. The air is heated until the temperature is 200 degC. Calculate the change in entropy...

Homework Statement One body of constant pressure heat capacity C_P at temperature T_i it's placed in contact with a thermal reservoir at a higher temperature Tf. Pressure is kept constant until the body achieves equilibrium with the reservoir. a) Show that the variation in the entropy of the...