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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Internal energy and photon absorption

I just wish to confirm whether my understanding is correct. I know that photon absorption/emission brings about quantised changes in electron energy levels. Photons (infrared) also interact with ...
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1answer
55 views

What really is a thermodynamic system?

I'm starting to study Thermodynamics and I'm pretty confused about what a thermodynamic system really is. When studying mechanics we focus our attention on systems of particles. So when we talk about ...
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3answers
89 views

Propagation/generation of sound is an isentropic process

Is the propagation and generation of sound an isentropic process? Is it because it is a reversible adiabatic process? Why would it be adiabatic? Does it happen so fast that there is no time to ...
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342 views

Why sound does not heat up the air?

Both thermal energy and air are propagated through vibration of particles so why sound does not heat up the air e.g loud musical instrument does not generate much heat ?
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43 views

Steady-state adiabatic nozzle, unknown exit velocity & temperature [closed]

The question is 2.10 taken from: Introductory Chemical Engineering Thermodynamics, 2E by Elliot,Lira Air at 30ºC and 2MPa flows ata steady state in a horizontal pipeline with a velocity of 25m/s. ...
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81 views

Difference between sound and heat at particle level

If heat (or thermal energy) are vibrations of particles and sound is a wave that is propagated through medium e.g vibration of air particles, what indicates if vibration of particles will be perceived ...
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31 views

Temperature change: boiling pasta in a lot of water or a little

SeriousEats gives a not-very-scientific representation of what looks like a thermodynamics calculation: Want to hear something even more interesting? Folks will occasionally say that "using a ...
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4answers
107 views

Difference between heat capacity and entropy?

Heat capacity $C$ of an object is the proportionality constant between the heat $Q$ that the object absorbs or loses & the resulting temperature change $\delta T$ of the object. Entropy change is ...
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36 views

Woodstove coppertubing heat exchanger [closed]

I am trying to use the excess temperature of my wood stove's stack to heat a copper tube heat exchanger with water running through it. The water is piped through my concrete floor for radiant floor ...
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1answer
67 views

Definition of entropy in nonequilibrium states

Thermodynamical definition of entropy $$S(p)=-\int p\ln p~dx$$ is defined only on equilibrium system. But why can't we use it for non-equilibrium system? Is there a well-accepted definition for it?
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185 views

Paradox while Cooling & Heating in Air? [duplicate]

I was thinking about how asteroids get "burned" up in the upper atmosphere as they approach the earth surface due to the atmosphere of earth heating the asteroids immensely as a result of air ...
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30 views

How to calculate the heat transfer rate between the liquid and the gas?

Let water (liquid) be in a chamber (with no heat transfer to the walls). The gas is the residual space above the liquid, meaning that the contact surface is the surface of the water. Given the gas ...
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53 views

Thermodynamics of scattering theory

I have a couple of conceptual questions regarding the thermodynamics of scattering. Any partial answer or argument will be appreciated. For the sake of discussion, consider the scattering of ...
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298 views

How do objects heat up?

If every body emits radiation at a given frequency and temperature exactly as well as it absorbs the same radiation, how do objects heat up?
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1answer
89 views

Are pressure and volume not independent properties in liquid water?

Every thermodynamics textbook teaches us that, for a simple compressible substance, any two independent properties will suffice to determine the system state. Those can be pressure and temperature ...
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82 views

Is there a minimum energy content of information, other than 0 Joules?

Lets say I want to send the bit string 010110 to someone. Is there a theoretical lower bound on the energy needed to do this?
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1answer
31 views

Spontaneity / Free Energy of Non-Isothermal Process

I'm trying to determine a lower bound for the work input necessary to make an entropy-reducing process "spontaneous" in the sense that the 2nd law is not violated. For a constant temperature and ...
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1answer
27 views

Showing the thermal expansion coefficient is the sum of the linear expansion coefficients

Given that the thermal expansion coefficient is defined as: $$ \beta=\frac{\frac{\Delta V}{V}}{\Delta T} $$ and the linear thermal expansion coefficient is defined as: $$ \alpha = \frac{\frac{\Delta ...
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1answer
39 views

$\mathrm{CO_2}$ rate of deposition

Parts of Antarctica average -127°F (-83°C). The freezing point of $\mathrm{CO_2}$ is -109.3 °F (-78.5 °C). If one could construct a large container at such a place shielded from the sun, would ...
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755 views

How cold would a bowling ball near absolute zero make a room?

If a bowling ball at absolute zero suddenly appeared in my room, how cold would the room get? Would I die? My initial estimation is that it one bowling ball at 0K (i.e., 300K below room temperature) ...
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32 views

Why do metal surfaces reflect thermal signature?

I recently borrowed a thermal camera from a friend and I tried to observe my palm print over a reflective metallic plate. When I looked at it through the camera, it reflected my thermal signature too. ...
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30 views

How are heat transfer rate and heat capacity constant of a material related?

How are heat transfer rate and heat capacity of a given material is related? When I was a kid I imagined it like "Capacity is like a container or bucket of some sort, if it gets filled easily it can ...
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55 views

How to model an apartment's airconditioning?

Background: This reminds situation reminds be of an episode from the The Big Bang Theory, although it is quite different from it. My roommate and I have similar temperature preferences and also share ...
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2answers
35 views

Followup to: The relation between energy quanta of an Einstein solid and the equipartition value of heat capacity

As a followup question to this question: The relation between energy quanta of an Einstein solid and the equipartition value of heat capacity and this answer ...
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120 views

Ice and liquid water interacting across a boundary

Imagine we have two thermodynamic systems, one a mass of ice and the other an equal mass of liquid water, with both at 273.16K. Each system is isolated, except that they can interact with each other ...
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1answer
49 views

The relation between energy quanta of an Einstein solid and the equipartition value of heat capacity

Consider an Einstein solid with quantized energy values $U=q\epsilon$ and $N$ oscillators. I calculated some values of an Einstein solid numerically through a function in R (at the bottom of the ...
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1answer
62 views

What are the contributions of the Non-equilibrium Thermodynamics?

I am very interested in Thermodynamics, but though it is easy to find good books and information about classical thermo, it seems that is not the same for non-equilibrium thermodynamics. I would like ...
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1answer
113 views

Why is everything colder nowadays? [duplicate]

I know that when the universe began it was incredibly hot. Ever since, it is been cooling, and nowadays the average temperature of the universe is quite close to 0 K. Is this a consequence of having ...
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149 views

Is the second law of Thermodynamics an immense tautology?

Let's imagine for a second a system that is changing constantly from one microstate to another one. It could be a given volume of a gas with its atoms moving and bouncing around, or a deck of cards ...
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250 views

Axioms behind entropy!

The concept of entropy is very ubiquitous, we learn about its uses starting from Information Theory (Shannon entropy) up to its basic definition in statistical mechanics in terms of number of ...
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22 views

Third principle of Nernst [duplicate]

I wonder how can I prove the fulfillment of the third principle of Nernst of a body that obeys the next expression.
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1answer
39 views

Scale down model of a refrigerator

I am teaching Thermodynamics. For teaching how refrigerators work I am looking for a working model of a scale down refrigerator. This should be as close to real as possible but very small in size. Can ...
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1answer
34 views

Calculating new temperature of an object when air temperature changes

I'm trying to calculate the new temperature of an object when the air temperature around it changes, given a period of time. Basically I get periodic readings from an air temperature sensor in a ...
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2answers
32 views

Latent heat of vaporization at non-boiling temperature

The latent heat of vaporization of water is what we normally use to calculate the heat transfer that occurs at 373 K when liquid water transits to vapor phase. But there are curves for latent heat of ...
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What are the thermal properties of a “perfectly rigid” container?

can a "perfectly rigid" container be a diathermal boundary? I checked the wikipedia article for heat and read: Kinetic theory explains transfers of energy as heat as macroscopic manifestations of ...
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1answer
55 views

If you dig a deep tunnel, will the rock sublimate?

If a tunnel is dug deep inside the crust (but before reaching places where the rock is liquid), how will the enormous downwards pressure manifest itself? Will the difference in pressure ...
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83 views

Is Rosehip Syrup boiling in a bottle?

My wife made Rose-hip syrup and the final part was boiling it in a saucepan. While still hot she placed it in a glass bottle. To keep it sterile she plugged it with a wine-saver top and sucked out ...
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1answer
106 views

Gravity and the Second Law of Thermodynamics [duplicate]

I was wondering about the hypothetical - and apparently improbable - heat death of the Universe when I stumbled upon this seeming contradiction. A certain volume of space with a uniform distribution ...
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1answer
37 views

Calculate heat transfer out of a basement

I am thinking it should be possible to calculate heat loss out of basement based on the temperature of the walls, but am not sure how to do it (what the equations are). For example, lets say the ...
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40 views

Quadratic versus other types of degrees of freedom

In my text book I have the following question and after thinking about this one for hours, I can't figure out what they're getting at: In Section 2.5* I quoted a theorem on the multiplicity of any ...
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1answer
22 views

Variable area manometer duct

How does one measure the pressure at the end of the manometer tube when the manometer tube itself is having a variable area?
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100 views

How many volcanic eruptions would be necessary per year to neutralize global warming?

Volcanic eruptions sometimes cool the earth. How many eruptions of what magnitude, locality and type would be required per year to neutralize Global Warming?
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How powerful would a series of rail guns or bombs need to be to destabilize a hurricane?

In an effort to destabilize hurricanes by burning the necessary cold zones it has been proposed that planes drop various carbon trash on them. That seems like a minor amount of heat change over a ...
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1answer
43 views

Partial Pressure - Which solution is right?

Question: Carbon dioxide (1.100 g) was introduced into a 1.00 L flask which contained some pure oxygen gas. The flask was warmed to 373 K and the pressure was then found to be 608 mmHg. If CO2 and O2 ...
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1answer
48 views

Irreversible work

I'm having some trouble trying to find the irreversible work done by a perfect gas when expanding. I know that the reversible work is greater than the irreversible one, but how can I find the ...
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2answers
45 views

Problem regarding heat engines [closed]

We have two different set ups: A 200K brick in a 300K environment A 300K brick in a 200K environment From which one of these can you extract more work? Assume equal mass and heat capacity. Using ...
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4answers
125 views

why are the square of the components of velocity equal?

In Principles of Physics by Resnick,Halliday,Walker, when evaluating the $v_{rms}$ ,they first found $p = \frac{nM(v_x)^2}{V}$ & then substiuted $(v_{avg})^2 = \frac{1}{3} .v^2$ where $v^2 = ...
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2answers
119 views

Who invented the perfume bottle thought experiment?

A common thought experiment used to explain the second law of thermodynamics, the "arrow of time", etc. is perfume escaping from an opened perfume bottle; the perfume is likely to diffuse into the ...
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1answer
95 views

Thermodynamics for Dummies: Entropy and temperature

I do not study physics and I have never had a course in thermodynamics. I have no idea what it is about, but I am currently taking a course where we had something about entropy. Would be great if ...
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2answers
126 views

Coarse graining on measurement vs phase space (second law)

I've followed Leonard Susskinds series on "the theoretical minimum". In the entropy/reversibility episode in statistical mechanics, he explains (at least one way of) how the apparent paradox of ...