Questions tagged [thermodynamics]

Covers the study of (mostly homogeneous) macroscopic systems from a heat/energy/entropy point of view. Consider also using tag: [statistical-mechanics].

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14 views

What does integrating the probability density function over all phase space gives us?

For a system of N-3D particles, we have 6N D.O.F and therefore a 6N dimensional phase space. I know that one point in phase space represents a possible state of the system. I also understand that a ...
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Question about the solution of problem 7-62 Thermodynamics Cengel 8th

A $25-kg$ iron block initially at $350°C$ is quenched in an insulated tank that contains 100 kg of water at $18°C$. Assuming the water that vaporizes during the process condenses back in the tank, ...
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Phase space, ensemble of systems and probability density function

I am trying to understand the concept of phase space in statistical mechanics. I can understand that a system, with $N$ total degrees of freedom, can be in different states, which correspond to ...
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Entropy change of an elastic cylinder

We had in our thermodynamics class an example regarding the entropy change of a rubber cylinder.It has an initial length $L_0$ and after we stretch it it has a final length $L_f$.A thermodynamic state ...
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In which cases you use free energy to calculate pressure?

From thermodynamic identity you get: $$\left(\frac{\partial U}{\partial V}\right)_{S,N} = -P$$ But with Helmholtz free energy $F = U-TS$, we can also get pressure from this equation: $$\left(\frac{\...
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76 views

Isn’t this a paradox?

Imagine a plate beeing irradiated from all sides with a specific wavelength. One side of the plate is smoth and reflects most of the incoming radiation, the other side is covered in grooves with the ...
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How cold would a neutron star to be to not give off neutrinos?

How cold would a neutron star to be to not give off neutrinos? I read this from Wikipedia and got interested. Unambiguous detection of individual gravitons, though not prohibited by any fundamental ...
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1st Law of Thermodynamics in a Filament

For a filament lamp that is operating normally such that the temperature is constant, the rate of change in internal energy of the system is zero. This would mean that rate of net heat transfer to the ...
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Why can I not feel the coldness of a cold wall at a distance in the way I can feel a warm wall at a distance?

As explained in this answer (https://physics.stackexchange.com/a/679166/295887) the human body according the Stefan-Boltzmann law of radiation is emitting radiation (mostly in the infrared region) at ...
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Apparent paradox in statistical mechanics

I can't understand why the likelihood of a particle to be in state $\epsilon_i$ in a canonical ensemble, does not depend upon the number of particles in that state. The probability that the a single ...
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Why does the Stefan-Boltzmann Law contain no information about the distance from the radiating body?

The Stefan–Boltzmann law states that the power radiated per unit area of a black body is equal to: $$ \frac{dP}{dA} = \sigma \cdot T^4 \,\,\,\,\,\,\,\left[\frac{W}{m^{2}}\right] $$ This power per unit ...
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Is conduction a mechanical wave?

A wave is defined as a disturbance which carries energy from one point to another point. In a mechanical wave, energy is carried by the wave from one point to another point by the vibration of ...
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Maxwell-Boltzmann distribution as the most probable

In Statistical Physics: An Introduction, by Daijiro Yoshioka, there's a neat derivation of the Maxwell-Boltzmann distribution as the most probable distribution of an Ideal Gas. He uses the method of ...
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What would be the proper distribution to model the number of particles in a state in canonical ensemble

Suppose my system has $N$ particles, and I want to find a distribution for $n_i$, the number of particles in the $\epsilon_i$ energy state. What I do know is the boltzmann probability, which tells me ...
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In the Hertz-Knudsen Equation, why does increasing the temperature decrease the evaporation rate?

Currently I am trying to understand the form of the Hertz-Knudsen equation, describing the evaporation rate (number of particles per unit time per unit area) from a liquid: $\frac{1}{A}\frac{dN}{dt}$ =...
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Calculating temperature change of of ocean if it absorbs 1K of temperature from the atmosphere

My practice problem reads “if the temperature of the atmosphere decreased by 1K everywhere, and the heat released is given to the top 100 meters of the ocean, the temperature of the ocean rises by $\...
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Stefan–Boltzmann law applied to the human body

The average person consumes 2000 kcal a day, which is equal to ~100 W. Furthermore, if one uses the Stefan–Boltzmann law to calculate how much someone loses heat due to radiation, it can be seen that ...
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Is steady state a necessary condition to apply Fourier's law of conduction? [closed]

In the derivation of general heat generation equation Fourier's law is applied but the 3d system is not considered as steady state system. So is steady state assumption necessary to apply Fourier's ...
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52 views

Does the second law of thermodynamics hold under non-equilibrium conditions? [duplicate]

The question is just that: whether the second law of thermodynamics is always valid under non-equilinrium conditions? The origin of life involves several chemical reactions that are thermodynamically ...
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Elastic potential of a balloon and pressure equilibrium

There are two different pressures acting on the surface of a balloon, the external one is clearly weaker than the internal one, so there must be a force that create equilibrium and avoid the balloon ...
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Are complicated equations and mathematical expressions really meaningful and realistic for explaining physical processes? [closed]

To further explain my question: One of the principles about doing scientific research that I will never forget, is the Occam's razor. Many famous scientists in the history also said something similar ...
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Can the lifetime of a broken covalent bond be calculated?

According to a paper (molecular dynamic simulation) published in 2018,(https://www.scirp.org/journal/paperinformation.aspx?paperid=83351) the Maxwell-Boltzman distribution is also valid for the number ...
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1answer
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When you reduce the pressure of a liquid below it's saturation pressure within a container, does it boil or evaporate?

I was playing around with a compressed air can, and it made me think of the greater physics behind what actually happens when I pull the trigger. I know that compressed "air" cans actually ...
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Confusion regarding Gibbs' paradox

I am trying to understand the following commentary I found in Wikipedia about this paradox: Now a door in the container wall is opened to allow the gas particles to mix between the containers. No ...
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1answer
49 views

Elastic collision of a ball against a container wall

I am writing a python script which calculates the final velocity of a ball after colliding with the wall of the container. The entire system is in 2D. The collisions are elastic, and the balls are all ...
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Is Gibbs/Boltzmann probability the 'true' probability of a particle being in a particular state in the canonical ensemble

Based on the classical interpretation of probability, the probability for a single particle to be in the $i$th energy state, in an $N$ particle system, should be given by the number of particles in ...
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Latent Heat in the Ising Model

I am confused about the (non)-existence of latent heat in the first order phase transition of the Ising model. Most textbooks talk about latent heat as a signature sign of a first order transition, ...
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1answer
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Equation for enegy loss from evaporation/sublimation in vacuum?

Imagine you have a solid that you are rapidly heating inside a vacuum chamber with some kind of thermal heater or a laser such that the material begins to evaporate or sublimate. Obviously radiative ...
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Entropy in a reversible process

According to 2nd law of thermodynamics entropy never decreases, it's either zero or bigger. The problem with the definition is that it doesn't specify WHICH entropy never decreases? Of the system that ...
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24 views

Gibbs free energy of mixing

If we have to ideal gases A and B in two chambers divided by a thin wall. $n_A$,$n_B$ are the number of moles for each gas. I need to find the gibbs free energy of mixing when I remove the barrier. So ...
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107 views

On the requirement of equilibrium in thermodynamics

I am currently watching a thermodynamics course offered by MIT. Here is the link: https://www.youtube.com/watch?v=kLqduWF6GXE&list=PLA62087102CC93765&index=2 From minute 18:00 until 19:10, the ...
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The entropy of Hawking Radiation

I am reading the review paper "The Entropy of Hawking radiation" by Almheiri et. al. They show the Page curve in the following figure: However, they do not show a formula of what they refer ...
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Heat and time to melt metal. What physics is missing from my model? [closed]

In order to determine the time it takes to melt a metal, I'm using the specific heat of the metal and the power output of the heat source. Based on the calculation, I think the resulting time is too ...
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Energy used to boil a full kettle once vs boiling enough water for a cup multiple times

I have an electric kettle and a thermal carafe. The carafe itself is not heated, it's basically just a large thermal flask. I've noticed that when hot water is kept in the carafe, the water stays ...
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Temperature coefficient

If we raise the temperature of any conductor the atom, free electrons starts vibrating There kinetic energy increases If kinetic energy increase then , Current must be increase As current increase ...
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Young's Modulus as a function of temperature

Is there a formula that relates Young's Modulus as a function of temperature? From Wikipedia, there is this formula in section 3.3: https://en.wikipedia.org/wiki/Young%27s_modulus I tried my best to ...
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Expectation value of energy in a canonical ensemble

Suppose we have a canonical ensemble system of $N$ particles, and $k$ single-particle-energy levels labeled by $\epsilon_i$. The energy of the different microstates of the entire system is given by $\...
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Why does water boil in bubbles? [duplicate]

When my glass kettle is boiling water, you can see all the bubbles going up in a line. Why do bubbles originate from a selected group of points on the bottom of the kettle? Why isn't it random? What ...
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Is the total energy of a canonical ensemble system of $N$ particles, with single-particle energy levels given by $\epsilon_i$ fixed?

Is the total energy of a canonical ensemble system of $N$ particles, with single-particle energy levels given by $\epsilon_i$ fixed ? We know the total energy of the system is given by : $$E=\sum_{i} ...
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Why do we need insulation material between two walls?

Consider a slab made of two walls separated by air. Why do we need insulation material between the two walls. Air thermal conductivity is lower than most thermal conductivities of insulating material ...
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Efficiency of electric heaters

I was reading this question. A person was asking what is the efficiency of an electric heater, and to sum up, people were answering "All resistive heating, can be considered to have 100% ...
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Does having a large liquid surface effect evaporation stability?

Imagine I have a metal block in a vacuum chamber, which is then heated by a laser. It is heated past its melting point until a small melt pool is present at the location of the laser. My question is: ...
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Interpretation of probability in Statistical Mechanics

In statistical mechanics, in particular the canonical ensemble, the probability of the system to have a particular state is given by : $$P_i=\frac{e^{-\beta E}}{Z}$$ Here $Z$ is the partition function ...
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What is wrong in my attempt? [closed]

The following question is a question from KTG and Thermodynamics. In this question I tried to solve it by finding the work done by the gas and equating it to $nR\Delta T$ but the answer turns out to ...
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How can I calculate to how fast heat is transferred from the surface of a massive hall to the ceiling?

I have asked something similar to this question before but couldn't get an useful answer: https://worldbuilding.stackexchange.com/questions/213240/i-am-building-an-isolated-indoor-temperate-rain-...
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Can Brownian motion explain why white smoke moves around in the air?

Can Brownian motion explain why white smoke (fume) generated by chemical reactions moves around in the air?
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What does ultra-rarefied gas mean?

Without using any math, can you explain to me what a rarefied gas is? And then what an ultra-rarefied gas is? I'd like to understand it from a conceptual level if you can make connections to other ...
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Exact heat capacity of the 2-dimensional Ising model

The following is a section from the book Newman, M., and G. Barkema. "Monte carlo methods in statistical physics" New York, USA (1999). and then: From those two quotes, it seems that there ...
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Confusion regarding the use of partition function

Suppose we have a system filled with $N$ particles. There are $k$ energy levels in this system, labeled by $\epsilon_i$, each with a degeneracy of $g_i$. Let us imagine $n_j$ particles out of these $N$...
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Adiabatic index knowing only $p$, $V$, $T$ in an adiabatic transformation? [closed]

1 mol of ideal gas is adiabatically compressed so that it's pressure becomes 32 times it's original pressure, it's temperature raising from 300 K to 1200 K. How do you find the adiabatic index here? I ...

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