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

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Thermodynamic equilibrium or thermal equilibrium and equipartition theorem

In all derivations of the equipartition theorem I can find a thermodynamic equilibrium distribution is used to show it's validity. But more vague sources (this site, wikipedia) state that only ...
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1answer
63 views

Does heat flow through a rod with a uniform current?

Consider a rod with uniform current flowing through it from left to right. Will heat flow throughout the rod or will the rod heat up uniformly? My thoughts are that no heat will flow, but rather the ...
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1answer
58 views

Why is entropy of system same for reversible and irreversible processes? [closed]

I read that entropy change of universe is zero in a reversible process but positive in a irreversible process,then doesn't it mean that entropy change of system of both the processes must be ...
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33 views

Meaning of $\frac{1}{\beta} \frac{\partial \ln{Z}}{\partial X}$ in arbitrary ensembles with X being a sharp Observable of the System

I often find the statement, that for an arbitrary ensemble with Observables $O_i$ of which only the mean value is known, and $\tilde{O}_j$ that are known exactly, the partition function ...
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1answer
28 views

Characteristics of a Particle reservoir

What does a particle reservoir mean in thermodynamics? How is it characterised? Heat reservoir for example, is characterised by temperature and supplies or absorbs any amount of heat without changing ...
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20 views

Black Body Radiation of a Home

If there is a home which is far away from all other buildings, what is the heat transfer due to radiation at night? Is the governing equation this: sigma*(T_home^4 - T_space^4)? Does the home radiate ...
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2answers
187 views

Why are sound waves adiabatic?

I want to know why we can treat sound waves as an adiabatic process. Precisely, I know that pressure and density vibrations occur so fast that molecules have no time to exchange energy (I might be ...
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0answers
43 views

Boiling Water in the Vacuum of Space [duplicate]

In space: When you depressurize ice with a temperature of -72 degrees Celsius would it turn into water? Is there a stable temperature range in which water stays liquid? Does the temperature ...
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1answer
60 views

Difference between state variable and state function in thermodynamic?

I think these two terms are sometimes used as synonyms and other times as different concepts. Can some explain what is the difference? An example would be good. Also, can state variable be the state ...
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2answers
79 views

Free expansion of an ideal gas

I am having trouble understanding the transient phase of an ideal gas expanding into vacuum. Firstly, the pressure of any gas is defined only when there is an instrument (barometer/ wall/ piston) ...
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2answers
128 views

1st Law of thermodynamics (conservation of energy) and quantum tunneling

Doesn't quantum tunneling contradict the 1st Law of thermodynamics? As far as I remember my school physics teacher told us that quantum tunneling is the reason why we can observe the alpha decay, as ...
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1answer
34 views

Water molecule Resonant Frequency

If water is subjected to microwave energy at the water's exact resonant frequency but 90 degrees out of phase, would the water molecule cease vibrating? Would the water then freeze or be cooled at ...
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1answer
30 views

No heat flow is to thermal equilbrium as … is to mechanical equilbrium?

When two systems are in thermal equilibrium, this means that there is no heat flow between them. What is the analogous definition for mechanical equilibrium? (I know that in mechanical equilibrium ...
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1answer
47 views

Conterflow heat exchanger with different flow rates

If we have tube in tube heat exchanger, in classic situation surface area in contact with both fluids is the same (if we ignore wall thickness of the tube). If fluids have significantly different ...
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1answer
38 views

Lead shielding very close to the Sun

I understand that eventually lead would melt when it nears the sun. In a liquid state how effective would lead be in blocking radiation? Would it still be as effective as solid state of lead? What ...
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1answer
42 views

How should I think of a liquid in terms of interatomic potential and molecular speed?

A rather simple question for liquids specialists I guess but I have hard time finding information about this. Here is my problem. I understand the ideal gas theory and the Maxwell's speed ...
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1answer
28 views

Adibatic process in QM and thermodynamics?

I have come over the phrase 'Adiabatic process' in two different contexts, that of QM and Thermodynamics . QM A adiabatic process is one is slow compared to: $$t=\frac{\hbar}{E_n-E_m}$$ and ...
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1answer
60 views

What does the solid phase in a two-dimensional system with Lennard-Jones potential look like?

Consider a system of two dimensional particles interacting via Lennard-Jones pair potential: $$u(r) = 4[(\frac{1}{r^{12}})-(\frac{1}{r^{6}})]$$ where r is the distance between two particles. What does ...
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2answers
64 views

How to conceptually identify reversible and irreversible processes?

When I studied thermodynamics for the first time I didn't really get much the conceptual understanding on reversibility, but nonetheless I've got a rough understanding and a mathematical criterion for ...
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1answer
24 views

Free energy been a minium confusion?

I know that if I hold the temperature and volume constant, then the Helmholtz free energy will try and be a minium. Now let us say I am doing a process changing the volume. Let us say at a point (i.e. ...
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1answer
46 views

How accurate is the following description (quoted) of what happens when a liquid is heated in a closed vessel?

"Boiling does not occur when liquid is heated in a closed vessel. On heating continuously vapour pressure increases. At first a boundary is visible between the liquid and vapour phases because ...
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0answers
14 views

Thermodynamics: state change and process types

Why is change of state, for example: water to ice, considered an isobaric process as opposed to isothermal? I had always learnt that temperature does not change during change of state.
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60 views

What is the difference between thermodynamic and empirical temperature?

When I've studied Thermodynamics I did so in Callen's book and there the author talks about temperature as a single thing, which mathematically is simply defined as: $$T = \dfrac{\partial U}{\partial ...
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1answer
40 views

Work done by the system

I have a trouble in understanding the concept of the work. In the closed system, Work done by system=Work on surroundings Here is the part of the process that prove "Work on surroundings=pressure of ...
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26 views

Isothermal expansion of a cavity containing electromagnetic waves?

The cavity is perfectly reflecting , and simulates a black body . Is it that during an isothermal expansion of a cavity containing electromagnetic waves the internal energy density is constant and ...
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2answers
75 views

The temperature of an electron

Does an electron have a temperature, if so, what is it? Imagine an electron (Ke = 1 eV) in a tube at room temperature (300 K) what is its temperature? Imagine now same electron in space (3 K) ...
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2answers
87 views

Boyle's Law-$ PV= nRT.$ What equation should be used to find pressure if n is not constant, like in an elastic system?

When air is added to an elastic system, like a balloon, the volume and pressure change. Would use Boyle's Law- $PV=nRT,$ but n does not remain constant in this situation. Known: $V_1$ is at ...
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1answer
197 views

Physics of boiling an egg - what am I missing? (heat capacity and coagulation question)

Update: 1) I originally posted this because the numbers seemed to make no sense to me (seemed very counterintuitive to only need 60-100ml of water to cook an egg when you usually have to boil it ...
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4answers
65 views

Why work is done on the system in this case?

Consider the following situation: The system is the air contained within a bicycle tire along with a tire pump connected to it. The pump plunger is pushed down, forcing air into the tire. Assume ...
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1answer
85 views

Deriving Enthalpy from Stat Mech

One can derive all the numerous thermodynamic potentials (Helmholtz, Gibbs, Grand, Enthalpy) by Legendre transformations, but I'm interested in seeing each from Stat Mech instead (ie taking the log of ...
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2answers
40 views

Definition of atmosphere unit and relation to temperature and gravity

I've seem sometimes the atmosphere unit for pressure be defined so that $1\ \mathrm{atm}$ would be the mean atmospheric pressure at sea level. I've seem on the other hand the following definition: ...
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53 views

Why does cold air feel even colder when you are moving through it quickly?

My question is the following: Why does it feel colder (i.e. why does your body transfer more heat to the surroundings) when you are moving through the air at a high velocity, f.ex. when you are ...
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1answer
33 views

Relationship between thermal conductivity and reaching the steady temperature

The diagram is for three materials with 3 different thermal conductivities, i think the material with higher thermal conductivity is the number 1 because it transfers the heat much better so it gets ...
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1answer
50 views

The average value of the electric polarization of an ideal gas

An ideal gas consisting of $N$ molecules possessing an electric dipole moment $\mathbf{d}$, placed in a constant electric field intensity $\mathbf{E}$. Need to calculate the average of magnitude of ...
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3answers
113 views

Which is the second law of thermodynamics?

There are many statements. https://en.wikipedia.org/wiki/Second_law_of_thermodynamics#Various_statements_of_the_law But how do they say the same thing ? I don't understand. Why all of them are the ...
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2answers
104 views

Why rough surfaces promote nucleation of CO2 in carbonated drinks?

Glassware with scratched/etched surfaces generate more bubbles (video 1, video 2). Why these rough surfaces allow easier heterogeneous nucleation?
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1answer
36 views

Pumping water vapor into liquid water [closed]

Do liquid water and water vapor count as different types of matter? How does Second law of Thermodynamics apply when I pump water vapor into liquid water? What would happen when water vapor goes into ...
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1answer
33 views

Internal energy. Mechanics and Thermodynamics

Internal energy is defined in thermodynamics as a function of state, in such a way that, in an adiabatic process, the variation of internal energy equals to the work done, regardless of the way it has ...
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what are the things that affect the ion mobility of a particular material?

what factors are important in ionic transition in a substance? please use easy word to answer as I am a high school student.
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18 views

Computing the energy of a heat source

My son and a friend are doing a science fair project on thermoelectricity. While they understand ZT, the figure of merit conceptually, they do not know how to calculate efficiency. It's easy for ...
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1answer
35 views

Transfer of heat from ice to water in a beaker

How does the transfer of heat takes place from ice below 0 degree celcius to water at room temperature? Does it take place by conduction? Does temperature of water rises uniformly throughout or it ...
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49 views

What is the relation between Clausius and Kelvin-Planck statement?

What is the relation between Clausius and Kelvin-Planck statement? In second law of thermodynamics, it is said that these two statement are equivalent and inverse to each other. Violation of one ...
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38 views

Validity of Gibbs-Dalton Law

I know that the Gibbs-Dalton law valid for an ideal gas mixture of ideal gas components. Does it also hold in the case of ideal gas mixture of real gas components? For example, could I say the ...
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0answers
28 views

Expressing thermal efficiency for a closed Brayton cycle in terms of static enthalpies

I have a Brayton cycle made of a compressor (stage 2 to 3), a heat exchanger (stage 3 to 4) and a turbine (stage 4 to 5). The turbine and compressor are connected through a shaft. The cycle is closed ...
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26 views

Ice and water mixed and entropy

In any introductory book, everybody has atleast done these type of questions where water at a high temp is mixed with ice and final temp and mass is asked with the understanding that zeroth law define ...
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91 views

Entropy change in a boiling egg

Yesterday in a rather intuitive Q/A session, by a visiting researcher in my town, this question got my attention.What he said was that if you boil an egg, the entropy inside the egg would increase.Now ...
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1answer
47 views

Heat and Thermodynamics [duplicate]

What is the temperature of air in the upper part of our atmosphere? I read somewhere that it is of the order of 1000 K, but then, why is it cold there? My question is different from the ...
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1answer
61 views

how is it proved $\frac{Q_c}{Q_h}=\frac{T_c}{T_h}$? [closed]

I know how to prove that the efficiency is $1-\frac{Q_c}{Q_h}$, but how do I go from that to $1-\frac{T_c}{T_h}?$ i.e. what is the proof that $\frac{Q_c}{Q_h}=\frac{T_c}{T_h}$?
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1answer
53 views

Can you concencrate paralel laser beams?

I've seen some videos of laser toys but they all seem to use either one laser or lens with some specific range of focus. What I was thinking is this: But it seems like it might violate the 2nd law ...
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25 views

What could be the anharmonicity effect if phonon interact with a tilted interface?

If Phonon propagates through c-axis grown structure and at the end reach a tilted interface of GaN, what phenomena will appear there? How anharmonicity is going to effect the phonon propagation ...