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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17 views

What decides the color of a flame?

Flame color can in part be decided by metal emission spectrums, that I know. But supposedly, the color could also be affected by the heat of the combustion, black body radiation. I’m wondering how ...
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Rubber band : Calculating work done using heat capacity at constant length

I am currently working through A Modern Course in Statistical Physics by Linda E. Reichl. (2nd edition) I am working on problem 2.8 which discusses a rubber band and am confused by part c) From ...
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Is there a thermodynamic process with constant internal energy but variable enthalpy?

Lately I've been trying to wrap my head around those two concepts and the difference between them. In an ideal gas, $PV$ is said to be an energy related to the kinetic energy of molecules boucing ...
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Explicit formula for entropy [duplicate]

Helle everyone, I have a question regarding the exact definition of entropy. When you look up te derivation (proof) of the Clausius-inequality, for example on wikipedia, the formula $$ d S = \frac{\...
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Regarding Paschen curves for Venusian air composition

I'm curious what the breakdown voltages look like for the venusian atmosphere, specifically at the surface of venus. How much power and voltage would be required to start an arc, and how much power ...
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“Tribo-Fatigue” Is this fringe pseudoscience or actual science?

Recently, while reading the wikipedia article on entropy, I came across "Tribo-fatigue entropy" in the interdisciplinary applications section this section seemed suspicious to me; even though there ...
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Time between collisions and collision time

I’m having a hard time really getting how the relationship between pressure and square mean velocity of a gas is derived for one single reason...seems like I don’t really know what impulse is. From ...
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Shape complexity of a substance and its effect on heat retention

While cooking, I have noticed that a ball of boiled spinach retains its heat for a long time. I understand that spinach is 91% water. It is my hunch that the same volume of water would cool much ...
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Question on a hypothetical cycle process in thermodynamics

The maximum (theoretical) efficiency a heat-engine can get, is given by the Carnot-efficiency, i.e. $$ e = 1 - \frac{Q_c}{Q_h} $$ It's obvious that if $ Q_c = 0$, the efficiency is $100$ %. Let us ...
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Why enthalpy change at constant volume is being stated as change in internal energy?

My textbook, NCERT Chemistry page-167 (PDF), states that change in enthalpy at a constant volume is give by: $$\Delta H = \Delta U =Q_{_V}$$ Whereas I think that it should be: $$\Delta H = \Delta U+...
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Forward Euler Method to solve Heat equation for two materials

In its simplest form the forward Euler solves the 1D heat equation with this equation. T(x+1,y) = (1-2r)*T(x,y) + r*T(x,y-1) + r*T(x,y+1) Where r = c *k/h^2, ...
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Proof that the static dielectric constant $\varepsilon_0$ is an intensive property

I am trying to prove (or disprove) my intuition that the dielectric constant, or equivalently the permittivity, is an intensive property. Does anybody have a proof or a suggestion for a method for ...
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Will inserting a partition into a thermally insulated box of ideal gas decrease the entropy?

Will inserting a partition into a thermally insulated box of ideal gas decrease the entropy? In the textbooks, they always say that the removal of a partition will increase the entropy, but what if ...
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Why is temperature and pressure constant during a phase transition?

During a phase transition, I have read that phase transitions occur at constant pressure and temperature. The explanations I have found both in books and online for this is that all the energy ...
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Which would keep you cooler? A black canopy tent or a white canopy tent?

I was outside recently at a function and they had two colours of canopy tent set up: black ones and white ones. I was wondering which one would be cooler to sit under. The white one would reflect the ...
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Detection and distinction of phase transitions

Are there established methods to detect phase transitions in experiments or Monte Carlo simulations, and when detected, to distinguish between first-order and continuous?
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How do I derive this formuale? This formula is found in carnot cycle in constant pressure? [closed]

This formulae is undergoing constant pressure processes and is a reversible heat engine.
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Harmonic Oscillators - Statistical Mechanics [closed]

"Consider a system with L states of discrete energy. Assume that the fundamental level energy, E0, has a degeneracy of M: (a) Show that for high temperatures, the average energy is equal to the ...
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Critical supercurrent

What is meant by the concept of critical current when talking about superconducting phase diagrams and transitions? How does this relate to critical field and temperature? Thanks
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LED heat radiation

Consider two bodies in space exchanging heat solely by radiation. Let's call them a star and a planet. If the star contains a heat source and the planet doesn't, it can be shown that temperature of ...
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Correct Boltzmann counting for the partition function for diatomic molecule

Would it be reasonable, given the following: to use a factor of $\frac{1}{2^N N!}$ as opposed to the standard $\frac{1}{ N!}$ for the correct Boltzmann counting term in the partition function for the ...
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For what type of process, we can use $dq=Tds$?

For what type of process, we can use $dq =Tds$? Reversible or irreversible? If only reversible, how do we replace $dq$ in $dq=dU+ PdV$ by $Tds$?
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Confusion about changes in temperature

If two bottles containing hot water are placed in a container for cooling purposes and water at 0 degree Celsius is used, instead of melting ice, the cooling is slower. I get that the ice is taking in ...
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How to avoid confusion of when to use and not to use the heat of fusion and condensation to get the amount of water in temperature equilibrium?

I'm not very sure of when should be used the heat of fusion and the heat of condensation for water. This happened when I attempted to solve a problem of this matter. The problem is as follows: A ...
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Would both life as well as elementary particles no longer exist upon “heat death?

Would the elementary particles in the standard model still exist upon “heat death”? Would electrons stop orbiting around the nucleus? Would the periodic table of elements still be relevant assuming ...
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Does entropy depend on what we can measure?

This idea has been bouncing around in my mind for a few days. The modern definition of entropy is "the number of microstates corresponding to a given macrostate": $S = k \log W$. In a thermodynamic ...
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Dulong-petit's high temperature heat capacity limit

As per Dulong-petits rule almost all substance has a higher heat capacity limit, approximately C= 24.94 J/molK. [solids C=Cp=Cv] But there are many substances(salts like Agcl,Cucl etc) whose heat ...
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Ideal Reversible Heat Engine Entropy

For an ideal reversible heat engine, what is the entropy change of the system (heat engine) after 100 cycles? What contribution does the heat engine make to the entropy change of the universe?
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Finding entropy of Nitrogen at low pressures

I'm trying to calculate the entropy of gaseous Nitrogen (assumed to be ideal) at a particular state in a thermodynamic cycle. I know the pressure, temperature, and specific volume, but all property ...
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In a kitchen experiment, you empty a tray of ice cubes into a bowl of water. After an hour [closed]

In a kitchen experiment, you empty a tray of ice cubes into a bowl of water. After an hour or so, when the mixture has come to thermal equilibrium, you notice a little more water in the bowl than you ...
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Is “Air-gen” really possible, and how is it different from perpetual motion?

"Air-gen", as seen in Nature (See here and here), supposedly extracts net positive energy from ambient air at equilibrium. Is this really possible? Doesn't this violate a law of thermodynamics ...
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Will water increase the internal pressure in a Ridgid vessel when heated to 550F IF my starting pressure in the vessel is 3,000 psi? [closed]

It is a real problem in a high pressure breech lock exchanger with a Hollow Welded Lip Seal. During the strength test at 5,000 psi water will become trapped between the gasket and the welded lip seal....
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Enthalpy of Reaction

If I've found the change in enthalpy of an explosion reaction, how would I go about finding the final temperature and pressure in a constant volume using the enthalpy of reaction, number of moles of ...
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First law of thermodynamics: internal or external pressure?

I'm taking my first course in thermodynamics, so my apologies if this is a rather silly question. I'm a bit confused about the pressure term in the formulation of the first law. The first law states ...
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Calculation for lowering temperature in a room… room-fridge with water mist? [closed]

I just want to make a room as cold as a fridge. Of course this might be unrealistic with water, but I really need calculations. I have a setup with one mister, which is simply a device that atomizes ...
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Is the movement of heated gas via combustion considered “work” and thus a form of mechanical energy?

I'm teaching middle school kids about energy, but I got curious for my own education: Does heated gas, as a product of combustion, produce mechanical energy or is this conversion (from chemical to ...
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Bifurcation of Van Der Waal equation for real gases

Van Der Waal's equation leads to a cubic equation in v of the form $$Pv^3-(bP+RT)v^2+av-ab=0$$ This equation has 3 roots for $T<T_C$ and one root for $T>T_C$ I understand why region ABCDE is ...
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Can an electric shower be considered an open quasi-static system?

An electric shower is a reservoir, of fixed volume full of water (no vapor), with an inlet flow of cold water, a heating resistance, an outlet of hot water. There may be some loss of heat from the ...
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Change in internal energy as in $mc_vT$ [closed]

A spring-loaded piston-cylinder device contains 1 kg of carbon dioxide. This system changes its state from 100 kPa and 25°C to 1000 kPa and 300°C. Determine the heat transfer and work ...
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What is the final temperature of Aluminium? [closed]

$1.1$ kg of Al with an intitial temperature of $92^\circ \mathrm C$ is dipped into $0.5$ kg of $\rm H_2 O$ with an initial temperature of $12^\circ \mathrm C$. What is the final temperature of Al?...
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Thermodynamic equilibrium criterion

I have a question about a characterization of thermodynamic equilibrium as given on German wiki article: https://de.wikipedia.org/wiki/Thermodynamisches_Gleichgewicht#Abgeschlossenes_System What does ...
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Given just a speed (or kinetic energy) distribution plot of particles, is it possible to calculate their entropy?

What can you deduce about the entropy of a substance by seeing the plot of the particle speed frequency in the material? I'm wondering how the two are related and how additional information you need ...
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Calculating the change of entropy for non equilibrium states

In "Heat and Thermodynamics" by Dittman and Zemansky, section 8.10 (7th ed.) it's explained how to calculate the change in entropy in a system going from a non equilibrium state to an equilibrium ...
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Computing the work (thermodynamics) [closed]

First of all sorry for my bad english - it is not my native language. Let's say that there is a process ($1 \rightarrow 2$) where $P \ T= \mathrm{const}$. How can we calculate the work done by this ...
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Mach number at the throat of Convergence-Divergence nozzle

Why is it important to have a Mach number=1 at the throat of Convergence-Divergence nozzle? What if the Mach number at the throat is less than 1? Is a modification in the nozzle design required then?
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What is maximal entropy?

I am confused about the meaning of maximal entropy. Is it maximal when all particles have same velocity or when there is a gaussian distribution of velocities? In simple words does the system tend to ...
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Problem from the Open Latvian Physics Olympiad 2019: “Reactive Reaction”

A rockets engine is supplied with a mass $m$ of hydrogen every second and just enough oxygen to burn all of the hydrogen. Determine the thrust force of the engine given that the exhaust openings cross-...
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Will a hole cut into a wood plank expand or shrink when wood swells?

Is is well known that a hole cut into a metal piece would expand when the metal is heated, just as if the piece would expand without the hole. Is it the same for a hole cut into wood, when the wood ...
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Microscopic definition of heat in the grand canonical ensemble

For a general ensemble, we define the entropy $S = k_B\left\langle -\ln p_i\right\rangle = -k_B \sum_i p_i \ln p_i$ and the internal energy $U = \left\langle \varepsilon_i \right\rangle = \sum_i p_i \...
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Carnot engine efficiency and entropy

I think I am not understanding a key concept about thermodynamics. I have worked out the heat and work changes for a particular Carnot cycle. In fact, there is no heat change as we have 2 isothermal ...

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