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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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Given two substances of different specific heats, how do you find the final temperature and these phase related things

Given two substances of different specific heats, how do you find the final temperature of them both, phase of either substance if there was a phase change, and how much either substance has changed ...
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How can a reversible path be substituted by a reversible zigzag path?

Say I have a thermodynamic process with parameters P,T,V [Pressure, temperature and volume], path starting from an initial state to a final state, to go back to the initial state we have to stay in ...
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Why do we have to dump the extra entropy created in a heat engine?

In his introduction to thermophysics, Daniel Schroeder writes the following about the process in a heat engine: Only part of the energy absorbed as heat can be converted to work. The reason is, ...
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Thermal Efficiency

For a thermally efficient house, is it better for the windows to be framed with something like aluminium, or steel? I am considering the thermal conductivities, aluminium has a value of 200, while ...
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I reasoned that if $T_2 > T_1$ then $E_1>E_2$. Obviously this can't be right, what is the flaw in my logic?

We have an entropy function and I've shown that for this function $T_1(E_1)=T_2(E_2)$. Further, the fact that the entropy function is concave is stated. There are two systems in contact and only ...
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Random walk with Ammonia molecule [closed]

This question is from Keith Stowe's Introduction to Thermodynamics book under Random walk. The question is something like this: I am aware that I am not supposed to post homework questions like this ...
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Conceptual question in thermodynamics about isothermal processes

If a process is isothermal then Δ U is zero. So ΔQ is non zero. But isn't ΔQ=nCΔT. Implying that ΔQ is zero. Where am I wrong? (Considering ideal nature)
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On isentropic compression of ideal gases, work and internal energy

I'm trying to understand something about isentropic compression of Hydrogen. If you are assuming constant specific heats, the work done during an isentropic compression is $$W = \frac{k}{k-1}\cdot ...
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Is the work done by friction considered as heat?

In the first law of thermodynamics, We write the change in internal energy in terms of heat exchanged and work done. The answer to the above question doesn't matter if our final aim is to find the ...
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On Joule's free expansion experiment

While reading through an introductory textbook in Thermodynamics, I've come across a series of arguments that seem somewhat arbitrary/vague, on which I'd like some clarification. To begin with, the ...
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What is the topology of a phase diagram?

Looking at various two-variable phase diagrams I was struck by that on every one I have seen so far all the phases formed simple connected regions; see, for example the phase diagrams of $H_2O$ or of $...
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Why is the number of excited vibrational modes $g(\nu)d\nu$ proportional to $x^2e^{-x}$ in Debye's theory?

I come across a problem in Terrell Hill's "Introduction to statistical thermodynamics" saying that: In the Debye theory, the number of excited vibrational modes in the frequency range $\nu$ to $\nu+...
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Periodicity trick for Kerr Black Holes

I am slightly confused concerning the euclidean section of a Kerr black hole. In page 5 of the following paper https://arxiv.org/abs/hep-th/9908022 it is said that in order to get the euclidean ...
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What's the difference between static and stagnation properties? [closed]

Difference between static and stagnation properties.
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Derivation of Proportionality of Phase Space Volume log(Γ)∝N

In the derivation of extensivity of entropy for the micro-canonical ensemble, we assume an ensemble of two systems with the energies $E_1$ and $E_2$. The total energy is given as $E<E_1+E_2<E+\...
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What was the informational content of the universe at the Planck time?

If the energy of $1 \, \mathrm{bit}$ of information is $k_{\small{\text{B}}}T \ln{2}$, then the energy of that bit increases with the temperature of the system. When I try to calculate how much energy ...
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Why does the energy of a thermodynamic system depend on the volume?

In thermodynamics one assumes that the energy (or other observables) of the system only depend on a few parameters like the temperature, the particle number and also the volume: $dE = \left(\frac{\...
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Interpertation of Motron Number

The Reynolds number is interpreted as the ratio of inertial to viscous forces in a flow. Are there similar interpertations for The Motron Number?
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Are waterfalls heating the planet?

This might seem like a really obnoxious question, but hear me out. During the last physics class, we determined that water that bursts down a 50m high waterfall undergoes $0.117K$ of temperature ...
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Question on convective heat transfer

Why is the following formula used when we define heat transfer due to convection on a flat plate?: $$ q=h(T_s-T_\infty)$$ Where $T_s$ is the temperature of surface at a particular location and $T_\...
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Potential Energy of Particles

I read the following statement in my textbook While a liquid is boiling, the energy supplied to the liquid goes to breaking the bonds between neighbouring molecules. Can anyone explain the process ...
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61 views

Pressure correction and volume correction in van der Waals' equation of state

I have a problem in understanding the van der Waals real gas equation and it goes like this. $$ nRT=\left(P+a\frac{n^2}{V^2}\right)(V-nb) $$ Do the variables $P$ and $V$ on the RHS have the same ...
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What is meant by finite harmonic oscillator?

What does it mean to take finite harmonic oscillator, In research article "http://iopscience.iop.org/article/10.1088/1367-2630/17/11/113015 ", we were finding effective number of cobosons in ...
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Atmospheric pressure, density and temperature variation with altitude

I'm trying to understand how one can calculate pressure, density and temperature of the atmosphere as a function of altitude. My assumptions are mostly sourced from https://en.wikipedia.org/wiki/...
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Degrees of freedom for diatomic molecules [duplicate]

I have a doubt in understanding about the degrees of freedom (dof) ......as I have learned dof is nothing but the necessary parameters to specify the location and configuration of a system.....if that'...
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Maximum information stored in nested black holes

The question goes along the lines of understanding how does the entropy-information additivity works when black holes are inside other black holes, including the special case where the inner black ...
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Why can we not use the specific heat to determine the work done on steam in a Rankine cycle?

Okay, I am trying to work backwards from an exam which I messed up and I am trying to figure out what the lecturer did based on his answers posted online. Looking back, I realise one mistake I made ...
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Question about carnot two phase power cycle

The figure below is based on material presented in an MIT OpenCoursware program on thermodynamics on the web. They were comparing a Carnot two-phase power cycle to a Rankine cycle with superheating (...
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Brayton Cycle PV diagram when regeneration is not possible

https://www.ecourses.ou.edu/ebook/thermodynamics/ch09/sec092/media/th090203p.gif Above is the case of ideal Brayton cycle when the temperature at exit of turbine ( state 4 ) is greater than the ...
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Show that having a thermodynamic potential in terms of its natural variables will give complete information about the system

I have only have one textbook on thermodynamics and this proof isn't featured (Fermi, only 140 or so pages) and my lecture notes say 'this proof is beyond the scope of the course...', but I'm curious. ...
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1answer
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Melting ice inside water by increasing pressure

An ice cube is floating in water inside a container and the system is in thermal equilibrium. And let say we somehow immerse the ice cube slowly into deeper region inside the container (we may pull a ...
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38 views

Does hot water turns to ice quicker than cold water? [duplicate]

I kept hot water by mistake in freezer and noticed that it turned to ice pretty quickly and then I simultaneously put hot and cold water in freezer, still the results were the same. How so?
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Champagne bubbles and gravity

One of the influences on bubble size is the speed with which a bubble rises in a glass - this, I believe, is due to the force of gravity which acts on the liquid around the CO2. The greater the ...
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How do you find the propagated uncertainty for the thermal expansion coefficient?

I am currently working on a lab report involving thermal expansion coefficients. The main idea of the lab was to identify materials based on their thermal expansion coefficient. Each material was a ...
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What is the most energy efficient way to heat and maintain the temperature in a tank (vertical column) of water with 4 heating elements? [closed]

1) Given the following tank of water with four heating elements in two groups, A and B, where the elements in each group are switched on and off together, what is the optimal way to heat the tank of ...
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Integrating Carnahan-Starling Pressure

Given the Carnahan-Starling equation of state for a solution of hard-spheres, $$ Z = \frac{P}{\rho k_BT} = \frac{1 + \eta + \eta^2 - \eta^3}{(1-\eta)^3}$$ where $\rho = N/V$ is the number density and ...
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In the value of gas constant $R$, what kind of mole is it?

Wikipedia gives $$R=8.3144598(48)\, \rm J\,mol^{−1}\,K^{−1}$$ But I want to ask how is it possible to write $\mathrm{mol}$ without a suffix? I mean, we must determine if we have $1\ \mathrm{mol}$ of ...
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Brayton cycle PV diagram with isentropic efficiencies introduced

https://imgur.com/4FKdiEN "PV diagram edited with Isentropic efficiencies for Brayton Cycle" I think that when isentropic efficiencies for compressor and turbine are introduced , the compressor takes ...
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Can't understand energy conservation in simple thermodynamics example

SITUATION Consider a very big cylinder with a mobile piston in the middle separating two sections (A and B) filled with gas. Both the cylinder walls and the piston are adiabatic, so there is no ...
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How is it possible that the earth has the concept of energy equilibrium: the same amount of energy comes in and out?

I was reading this article on the Earth's Energy Budget, as well as a few other articles that basically contained the same information: That there must be an equilibrium of energy coming into the ...
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Computing the average energy $\overline{E}$ in thermodynamic equilibrium for a paramagnet

I am having trouble with the following physics exercise: In the case of a paramagnet in a magnetic field $H$, show that from the requirement that $F(E)$ (the Helmholtz free energy) be minimal in ...
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A question on firewall paradox?

In the firewall paradox, one considers a Hawking particle pair after the Page time. Assuming information conservation, the emitted particle must be entangled with early Hawking radiation. Assuming ...
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Efficiency of a Carnot machine, in which, some of its extreme points are in the region of liquid transition to steam

I need to calculate the efficiency of a Carnot machine, in which, some of its extreme points are in the region of liquid transition to steam with the works, differences of energy and heats of each ...
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Could we harness the energy from room temperature? [closed]

If no atom is at absolute zero, it must have kinetic energy. Therefore, could we harness that energy, (sure for small objects, not much energy would come of it) but surely the earth itself has a ton ...
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Energy of light rays under First Law of Thermodynamics [duplicate]

There is increase in the wavelength of light from distant quasars as it reaches us, due to the constant expansion of the Universe, or so I understand. In that case, due to increase in wavelength, the ...
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1answer
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Variation/Differential in Critical Radius of Homogeneous Nucleation

Getting the critical radius during nucleation from G(r) is straightforward - but in our lecture notes, a notation is used that I cannot quite wrap my head around: The molar Gibbs Free Energy $G(r)$ ...
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Computing the Helmholtz free energy for a harmonic oscillator

I would like to calculate the helmholtz free energy for a harmonic oscillator, which has energies given by the equation $\epsilon_{n} = n\hbar\omega$, where $n$ is a natural number greater than or ...
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Replacing Qh with Ql in Etropy equation in Heat Pump

In the heat pump below, the $T_H$ is not constant. It is assumes that the process is steady and reversible. So when constructing an entropy equation over the CV (the purple-colored area): $$\dot ms_1+\...
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How does the internal resistance of a cell vary with temperature?

Does anyone have a physics explanation to why the internal resistance of a battery decreases as the temperature increases?
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In Boltzmann distribution, why is the system at the same temperature as the reservoir?

Consider a boltzmann distribution where the total energy of the reservoir and the system is $E$. The energy of the system can be $\epsilon_i$ and the energy of the reservoir is $E-\epsilon_i$. Now ...