Entropy Definition and 999 Threads

Bell's theorem debunks theories concerning local hidden variables. Many people interpret that as the complete absence of local hidden variables. Hidden variable theories were espoused by some physicists who argued that the state of a physical system, as formulated by quantum mechanics, does not...

I have trouble understanding why we classify an inviscid adiabatic incompressible flow along a streamline as isentropic I understand this from a Thermodynamic definition/explanation $$dS = dQ/T$$ Adiabatic Invsicid $$dQ =0= dS$$ So no heat added or lost no change in entropy I'm fine with that...

Hi community, I'm trying to get my head round all these concepts. So entropy is given by S= k ln W. where W is the number of microstates of a system. Know let's imagine there is a box containing a number of gas atoms let's say the gas atoms have a current position and velocity and say you can...

I'd like to create a simple model that demonstrates the basic values of thermodinamics of an ideal gas. I begin with two rooms, several molecules in them. Every data of every individual molecule is given (position, mass, speed, etc), so I can easily calculate the total energy, pressure...

Hi. I read this thread with great interest and have similar question: In a deterministic universe, does entropy exist for Laplace's demon? Since he knows the universe to it's microstate, does the term "macrostate" even make sense to him? And say there is a "half-demon" that only knows the...

Let's imagine a deterministic universe. A one where quantum mechanics simply doesn't apply. Ok. This was the universe of classical physics. Atoms exist, and they behave deterministically. Fine. Now, how can entropy increase in this universe, altough it has the same laws of physics. In a...

Is there any way to measure time without reference entropy? i.e suppose the universe has maximum entropy , is there any way to define a sense of time "after" that?

Homework Statement Hello, i am given an isothermal transition for nitrogen, N2, where temperature is constant at 700K, p1=1bar, and p2=100bar. For this problem i am not allowed to use any equations of states, such as Benedict-Webb-Rubin, or Beattie-Bridgeman. Rather i am given only Cp data...

Hello, folks! So, I've come across this question on my Physics homework, and I'm not entirely sure how to finish all the parts. I've included the parts I've gotten correct and what I've gone to get those answers. Use the exact values you enter in previous answer(s) to make later calculation(s)...

What is the proof of the fact that for an isolated system, entropy can never decrease?

Hello, Few years back I was reading about calculating multiplicity using hypercube (n-cube). Multiplicity was normalized using this method. I wanted to read it again but I just cannot find it now. I tried every combination of keywords. I remember it was a Wikipedia link. Any help would be...

A closed, well-insulated container is filled with 454 g of water at 94.4 °C. To the hot water, 200 g of water ice at exactly 0 °C is added. The mixture reaches an equilibrium temperature of 41.1 °C. Assume the molar heat capacity is constant and all the processes are at constant pressure. The...

Hello everyone! I am an undergraduate student from Greece in my first semester of Mechanical Engineering, but I am fascinated with physics. I've been studying some physics books from my university's library and reached the chapter of entropy. I understand the 2nd law of thermodynamics but what...

When we talk about entropy, we say it comes from our inability to completely describe the state of a system. Also, we say it is a property of the system (like entalphy). That's confusing me a lot. If entropy is a property, how can it come from our inability to describe the system? Or it's just a...

Homework Statement The problem requires me to find the entropy of a diffusion constant as a function of time (I guess in terms of diffusion coefficient) Homework Equations Perhaps Heat / Diffusion kernel S = k p lnp The Attempt at a Solution I assume it was a delta initial condition then...

I learned that $$ dS = \frac Q T$$ In free expansion of Ideal gas, it is obvious that Q = 0. However, the entropy increases. I guess the reason is that it is because the process is not quasistatic. If I am right, why is this process not quasistatic. If I am not, what's wrong with the formula...

Hello, I have to find the density of probability which gives the maximum of the entropy with the following constraint\bar{x} = \int x\rho(x)dx \int \rho(x) dx = 1 the entropy is : S = -\int \rho(x) ln(\rho(x)) dx L = -\int \rho(x) ln(\rho(x)) dx - \lambda_1 ( \int \rho(x) dx -1 ) -...

Hello, In my textbook I read this example: A gas in an isolated system expands after pulling out a separating plate, so its volume increases and there is no work or heat exchange. the entropy of if the ideal gas is $$\Delta S = n R \ln \frac {V_1} {V_2}$$ and the second law of thermodynamics...

When calculating heat transfer, how would one know when to use Q=T*m*(delta s) versus Q=m*(delta h). I'm confused when we should calculate using entropy versus enthalpy. Anything helps. Thank you!

Homework Statement 52 distinguishable particles have been in a box long enough to reach equilibrium. The box is divided into two equal-volume cells. Let's say that there are 103 sub-states (s1 through s1000) available to each particle on each side, regardless of how many other particles are...

I am trained in aeronatical engineering, spent a number of year supporting sounding rockets in the exploration of the Upper Atmosphere. Retired 16 years ago. Am interested in General Relativity and Quantum physics. Looking to explore and understanding of entropy... Black holes... Etc.

Interesting TedTalk from Sean Carroll last month. At the end he asks the question of whether the big bang was really the beginning. Is this simple multiverse talk? Thoughts?

Homework Statement For a diatomic gas near room temperature, the internal partion function is simply the rotational partition function multiplied by degeneracy ##Z_e## of the electronic ground state. Show that the entropy in this case is ## S = Nk\left[ \ln \left(...

This video explains the entropy concept as in terms of useless and useful energy. My question is how is this concluded from say Clausius' statement of 2nd law of thermodynamics which states that there can exist no cycle that transfers heat from A to B without producing any other effect. I...

Homework Statement A gas obeys the equation of statez=1/(1-b(molar density)) What is the molar entropy change of expanding this gas from a volume of 1 dm3 to 2 dm3 at a temperature of 300 K, given b = 0.2 dm3? Calculate your answer to three significant figures and select one answer from the...

I was helping my cousin with her Physics II class and they just started discussing entropy in the Thermo section of the class and her teacher gave the "measure of disorder in a system" definition which I personally hate because even though it might be technically accurate, it doesn't really...

I learned about entropy is chemistry, can someone please explain how this term is used in physics? Thanks.

Homework Statement [/B] I was given a graph in the PV plane of a cyclic process and asked to find some quantities, one of them is the change in entropy for the system. I just had a question about the units. Homework Equations dS = CVln(Tf/Ti) The Attempt at a Solution The data was given in...

Homework Statement A composite system consists of an insulated partitioned volume, shown in Figure 4.9. Side 1 contains 2 mol of a monatomic ideal gas and Side 2 contains 4 moles of the same monatomic ideal gas. Initially, the two sides are separated by a fully insulated partition (adiabatic...

I recently posted a statement that according to the 2nd law of thermodynamics, entropy always increases in a closed system, no matter how small the time interval is that one looks at. I think that is true for classical thermodynamic models, please correct me if I am wrong. Does quantum...

The stars formation decreases the entropy but the radiations given out increases the overall entropy i am said ...but once the fusion processes are over the star no longer gives out radiations...and still the volume in which the matter particles of the star can be becomes less as the star...

I am learning physics on khan academy and they do a proof to show that delta G for a reversible reaction is negative and how for a irreversible reaction it is positive. However in the proof, they assume that the heat put in by the isotherm is less for an irreversible reaction compared with a...

Homework Statement An ideal gas with adiabatic index γ is taken around a complete thermodynamic cycle consisting of three steps. Starting at point A, the pressure is increased at constant volume V1 from P1 to P2 at point B. From point B to point C, the gas is allowed to expand adiabatically...

Homework Statement Consider a thermally insulated resistor with resistance R=20 Ω and mass m=5.0 g. The resistor is made of a material with specific heat capacity c=850 J/(g-K) and carries a current of 2.0 A for a time period of 1.0 s. a) Calculate the increase in the temperature of the...

<Moderator's note: this is a spin-off from another thread> Matter isn't spreading out because of gravitational attractions between matter. If you took a bunch of gravitating particles and sealed them in container, the highest state of entropy is one where all the particles coalesce, which...

In the Boltzmann entropy formula , the number of microstates is calculated according to Maxwell-Boltzmann statistics , i.e. , W = n!/Πki! , Σki = n . Why cannot we use some other method , such as Bose-Einstein or Fermi-Dirac statistics ?

the second law of thermodynamic state that their will be more chaos, and natural selection in the opposite of that. maybe this is a stupid question but can somebody anser this

Hi guys, I'm struggling to understand why an increase of entropy is directly linked with a decrease of total (stagnation) pressure. I have an idea, but I'm not sure if this is right. My understanding of the problem is as follows: Shear stress (friction) is a part of the entropy production term...

Because entropy and the often misled understanding of it shows up on PF on a regular basis, I thought it might be interesting to read about the history of how it all began. (Sorry, there wasn't an abstract to paste in here. But it's only four pages anyway.)...

I want to generate very random numbers. There's a few approaches to this, such as the audio input from a de-tuned radio, hooking user input such as mouse movement and hashing the results over a period of time etc.. My idea was to get a cheap Geiger Counter and just leave it monitoring background...

I'm reading Thermodynamics: Foundations and Applications by Gyftoploulos and Beretta, because the authors claim to give a presentation of classical thermodynamics without "... the lack of logical consistency and completeness in the many presentations of the foundations of thermodynamics" [from...

Homework Statement A mass m is thrown from a height of h. Find the entropy change of the mass, the surroundings and the universe. The temperature of the surroundings is T. Homework Equations dS=dQ/T ΔU=Q+W The Attempt at a Solution The main thing I don't understand in this question is how we...

Homework Statement A current ## I=0.2 A ## flows in a resistor ##R = 50 Ω## immersed in a rigid adiabatic vessel that contains ##n=3## moles of Helium. The initial temperature of the system is ##T_0 = 27 °C##. The resistor has a mass ## m = 10 g## and specific heat ## c = 0.2 (cal/K)/g ##...

consider an irreversible cycle. There will be no changes in the state variables (like U, S) of the system undergoing the cycle, but for the surroundings, there will be change in the state variables, in fact, entropy increases. my question is, what happens to the internal energy of the...

Dear All, I am trying to understand the concept of "entropy" in thermal engineering point of view. I have basic idea about "entropy" i.e. the change in entropy is used to determine the direction in which a given process will proceed. However following two more definition (of entropy generally...

Chestermiller submitted a new PF Insights post Grandpa Chet's Entropy Recipe Continue reading the Original PF Insights Post.

Maybe my question is a bit more philosophical than scientific. In the macroscopic world entropy means that things become more chaotic and less orderly as they decay. It seems to me somewhat paradoxical that in the quantum world lower generation particles "decay" into the first generation...

Hi. I have heard this, that entropy is often called "disorder" but _isn't really so_. And I am even more puzzled by the connection and difference between entropy from "information theory" pov and from "thermodynamic" pov. I see stuff like this...

This is an observation I'm making that seems like it is wrong but I can't figure out why it would be. Entanglement links two states together. For example the spin angular momentum of particles. An entangled state of two particles could be where you know if one particle is measured spin up the...

Hello - I just starting out in chemical engineering. I hold a batchelor's degree in Chemistry, and am making a transition to ChemE. This isn't for any class, just in general for reference, does anyone know of a good book that is primarily just thermodynamic charts, like T-S diagrams? I have...