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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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Relation between vapor pressure, temperature and boiling point of Freon

Below is a picture of a pressure gauge mounted on a Freon (R-134a) cylinder for precise recharging of air conditioning systems. It clearly shows a relation between Pressure and Temperature. Is this ...
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Smallest possible black hole containing any information?

My apologies for the meandering nature of this question. Using some back-of-the-envelope numbers: Planck length ≈ $10^{-35}$ m Planck area ≈ $10^{-70}$ m Radius of a black hole with a surface area ...
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What is the meaning of $PV^\gamma=$ constant in an adiabatic process?

In an adiabatic process, heat transfer doesn't occur and hence $\Delta U=-W$ (an increase in internal energy due to work done on the system or a decrease in internal energy due to work done on the ...
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Liquid and Vapor Density Evaluation During Cavitation

My understanding of cavitation, for a single pure fluid, is that for a fixed temperature when pressure drops below the vapor pressure the mixture state travels down a spinodal where it's possible that ...
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Could magnifying glass produce enough steam to recharge electric car's batteries in sunny countries

If you had a way of tracking the suns position, could a magnifier be used to create enough steam in a closed steam generator to produce enough energy to recharge electric car's batteries? I imagine ...
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Could the Landauer principle be circumvented in this way?

The Landauer erasure principle states that to erase a bit of information from a system, the entropy of the environment will be increased by at least $k_B\log2$, or equivalently, it costs at least an ...
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Why do we prefer to write free energies as functions of particular state variables? [duplicate]

Anyone who's studied thermodynamics knows the fundamental relations for the various free energies: \begin{align} \mathrm{d}U &= T\:\mathrm{d}S- p\:\mathrm{d}V\\ \mathrm{d}F &= -S\:\mathrm{d}T- ...
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Heat flow in response to a thinning barrier

I'm having a technical problem of heat transfer that I can't find the best approach to deal with. I'm grateful for any advice that can point me in the right direction! Here is an idealised model: ...
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Difficulty in calculating effusion rate using the kinetic theory of gases and statistical mechanics

I have tried multiple sources and methods, but my attempts at a proof of the number of particles leaving a gas using statistical mechanics keep finding the same wrong result. I have tried to read ...
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Gibbs Energy of Mixing, Issue with Equilibrium

In the problem below: But my question is, in the final state of this mix. Is not the system supposed to be in an equilibrium? Gfin shouldn't be 0? In that case Gmix=-Gi
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Trying to disperse heat from a heater [on hold]

I'm currently trying to find a way to "stop" a baseboard heater. As of now my heater is broken, and my dorm is extremely overheated. I've contacted the University that I attend and they sent someone ...
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Confusion while deriving kinetic-molecular theory of gases

How many of the molecules will collide within a given area A of the wall normal to the x-direction in some fixed time interval Δt ? On average half the molecules have a positive x-...
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Can the electromagnetic radiation pressure $p=u/3$ be the thermodynamic one $p(T)=u(T)/3$?

Can the electromagnetic radiation pressure $p=u/3$ be the thermodynamic one $p(T)=u(T)/3$? In electromagnetism, the radiation pressure formula $p=u/3$ does nothing with temperature at all. One quick ...
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How does the 2nd Law of Thermodynamics demand the existence of at least two thermal reservoirs in a cycle?

In my studies, I've come across Kelvin's statement of the 2nd law: It is impossible to undergo a cyclic process whose only effect is removing heat from a reservoir and generating an equivalent ...
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Why does increasing the volume in which a gas can move increase its entropy?

Let's say we have a box with a non-permeable wall separating the box in half. There is gas on the other side of the wall. Now we remove the wall so that the gas can diffuse to the other half of the ...
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Will having two water pans in my smoker make any difference?

I have a backyard smoker, and I use a tray of water in it as thermal mass to help keep the temperature stable. I don't think the size of the tray is going to matter, but it's roughly 40cm x 30cm x ...
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Pitch change opening thermos flask

If I return to my (closed) thermos flask for some more coffee, I hear a ringing sound as I open the flask (it is all metal), but the pitch of the ring increases as the sound fades - duration on the ...
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Internal energy of a system and its conservation

In textbooks of thermal physics, we usually find internal energy of a system defined as the energy measured in the center of mass frame. Now, in mechanics, we study the conservation of mechanical ...
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$\dot{W}_{lost}$ due to irreversible processes in the condenser of a refrigeration system

The condenser of a refrigeration system steadily admits $\dot{m} = 50 g/s$ of saturated R134a with a pressure $P_1 = 650kPa$ and a quality $x_1 = 0.9$. The condenser rejects $\dot{Q} = 7kW$ of heat to ...
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How does the door itself play into heat conducted from one door handle to the other?

I imagine have the door plays somewhat of a role and was curious what the terminology would be. I imagine be a bit too complex to simplify into a math formula.
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Confusion with entropy change associated with thermal reservoirs in an isobaric process [on hold]

On chapter 8, Entropy, Zemansky and Dittman's book Heat and Thermodynamics has a problem with following details: A body of constant heat capacity $C_p$ and at a temperature $T_i$ is put in contact ...
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Fluctuating Thermodynamic Properties in an ensemble

I am trying to determine what the fluctuating thermodynamic properties are in the (µ,P,S) ensemble. However I'm really not sure how to determine that. I do know that the corresponding thermodynamic ...
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How to calculate the time to uniformly heat an object by natural convection?

I want to heat a piece of steel in a muffle until I bring it to a uniform temperature. The idea is to preheat the muffle to a certain temperature and then place the piece in it and wait for it to get ...
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Can anyone explain equivalence of statistical entropy and thermodynamic entropy?

I read on wikipedia how Clausius came to define entropy after studying the Carnot cycle (He found a relation between heat transfer and temperature which was a state function,and named it entropy) but ...
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Does bag size and volume affect heat loss rate? [on hold]

Same size of ice cream been placed in small insulation and big insulation bag respectively. Whixh bags of ice cream melts first? How can we explain about the correlation of bag size and melting rate?
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Can indistinguishable microstates evolve into different macroscopic states?

I guess this question is more about definition than about any physical principle. Can a given physical system (or can there be a physical system) admit microstates that have identical macroscopic ...
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56 views

Can the universe build itself back together after the Heat Death? [on hold]

We all know that due to the 2nd Law of Thermodynamics the universe after a certain long period of time will eventually have all its energy spread out homogeneously and reach a Heat Death where nothing ...
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How to quantify the mixing of two hard-spheres gases?

Suppose that there are two types of hard-spheres gases ($a$ and $b$) in a box. Suppose that their radius is much smaller than the box's characteristic size. These two gases tend to repel each other. ...
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Is the specific heat capacity the same between real and ideal gases?

From Section 2.4.1 of this link where the change in the specific internal energy of a gas is given as $d u = \frac{\partial u}{\partial T} dT + \frac{\partial u}{\partial v} dv $ They define ideal ...
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37 views

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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1answer
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Random walk with Ammonia molecule [on hold]

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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1answer
48 views

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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Thermodynamics and classroom [closed]

The temperature of a classroom with dimentions of 10*8*3 m ia to be maintained at 23 degree. there are 30 students and a teacher in the room. the metabolic rates of a student and a teacher are 320 kj/...