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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Does Earth's loss of internal energy to the moon reduce local entropy?

The moon's orbit is increasing 3.78 cm/year due to the faster spinning Earth and tides pulling on it. The Earth slows down 15 microseconds/year. From this I've estimated (assuming the core's rotation ...
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1answer
24 views

Heat pump solution to pollution

I have invented a process that converts an air conditioner into a heat pump. How many metric tons of carbon equivalent could be eliminated from entering the atmosphere annually if 1.every air ...
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13 views

Prove for ideal gas temperature being directly proportional to absolute temperature [on hold]

I have some difficulties proving that the ideal gas temperature is directly proportional to absolute temperature defined by the second law of thermodynamics. The ideal gas temp. is defined by the ...
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1answer
45 views

How does the fundamental assumption of statistical physics make sense?

Consider two systems A and B in thermal contact. System A has $N_A=3$ simple harmonic oscillators and the system B has $N_B=3$ simple harmonic oscillators as well. Each system has a number of energy ...
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21 views

Exhaust liquefaction in internal combustion engines

Does an internal combustion engine provide enough efficiency to still deliver mechanical power, if it is forced to liquify it's own exhaust gases by compression? If gas containers would be added to ...
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1answer
17 views

What is the correct statement of Kirchhoff's Law of Thermal Emission?

There are various quite different statements in textbooks and other science literature as to Kirchhoff's Law of Thermal Emission. So, what is the correct statement of Kirchhoff's Law of Thermal ...
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102 views

How do we define temperature?

I was watching this video What is Temperature?. It states that when we measure temperature we are measuring $dU\over dS$ at equilibrium. But at equilibrium, how the entropy and the internal energy are ...
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1answer
34 views

Reduced Pressure and Cooling

Hi Knowledgeable folks, Since boiling point of a liquid can be reduced via pressure reduction. I was wondering whether this is possible: Add some liquid (alcohol or Water) in a container, reduce the ...
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1answer
24 views

Question on the degeneracies of a thermodynamic system

I think I have a basic understanding of what degeneracies are: Two or more different states of a quantum mechanical system are said to be degenerate if they give the same value of energy upon ...
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8 views

dry adiabatic lapse rate

Adiabatic lapse rate is defined as $$ \Gamma_a \equiv -\left(\frac{dT}{dz}\right)_{\rm parcel}=-\frac{R_{\rm a} T}{c_p \,p}\left(\frac{dp}{dz}\right)_{\rm parcel} = \frac{g}{c_p} $$ $R_a$ is gas ...
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1answer
28 views

work done in reversible and irreversible process

According to maximum work theorem work done maximum work is done during reversible process . consider a reversible adiabatic and irreversible adiabatic process that occurs between two states of the ...
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1answer
15 views

How quickly does the temperature rise in a water container submerged in a hot water bath?

Let's assume I have a small bottle (neglecting any insulation from the walls of the bottle) containing e.g. 150ml water at 4°C and place it in a larger pot with sufficient water at 80°C so that the ...
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27 views

Obtain an exact expression for the heat capacity of the system

Before anyone mentions it, yes I did my research and found this question on this site. My question is his exact question, but I'd like some clarification or maybe a bit more explanation than the one ...
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1answer
24 views

Number and energy density integrals in cosmological thermodynamics

I am working through Mukhanov's book "Physical Foundations of Cosmology" and something has me puzzled in the section on evaluating integrals for number density, energy density and pressure. The ...
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16 views

specific heat capacity (temperature) [on hold]

A 60KG bushwalker is suffering from hypothermia, having an average temperature of 33.5degrees.when rescued she was wrapped in a warm blanket and given two 310ml cups of warm tea each at a temperature ...
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19 views

Latent Heat of Vaporisation [on hold]

Is there a diagram which shows the effect of reducing pressure on Latent Heat of Vaporisation of water. Thank You.
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23 views

Specific Heat capacity [on hold]

The total heat capacity of a caloriemeter, heater, stirrer is 107 joules per kelvin. Mass of the liquid in caloriemeter is 0.241 kg. The power supplied by heater is 41.48 watts. The initial rate of ...
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1answer
66 views

Gibbs entropy, Clausius' entropy and irreversibility

I have a bunch of doubts and confusions on the concept of entropy which have been bothering me for a while now. The most important ones are of a more technical nature, arisen from the reading of this ...
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3answers
57 views

Is the internal energy of an ideal gas always $\frac{3}{2}nRT$?

Is the internal energy of an ideal gas always $\frac{3}{2}nRT\,?$ I saw in Wikipedia that it is $\alpha nRT\;.$ Is $\alpha$ always equal to $\frac{3}{2}$ for an ideal gas?
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Is Planck’s proof of Kirchhoff’s Law of Thermal Emission false, and if not why not?

In his book ‘The Theory of Heat Radiation’, Max Planck adduced his theoretical proof of Kirchhoff’s Law of Thermal Emission. It was recently shown that Planck’s proof is false: “The Theory of Heat ...
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15 views

Understanding the concept of temperature vs. mean energy/heat capacity of a system

I need help understanding a concept in thermodynamics. What is the relationship between temperature and mean energy? What is the relationship between temperature and heat capacity? What I know: ...
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1answer
51 views

Why the 3D heat equation is $\frac{\partial u}{\partial t}=\alpha\nabla^2u$ [on hold]

Why the 3D heat equation is $$\frac{\partial u}{\partial t}=\alpha\nabla^2u=\alpha\left(\frac{\partial^2 u}{\partial x^2}+\frac{\partial^2 u}{\partial y^2}+\frac{\partial^2 u}{\partial z^2}\right)?$$ ...
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61 views

Light from Absolute 0 [on hold]

Would matter that is cooled closest to instant to a near 0 temperature emit light?
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28 views

What constitutes an answer to a physics question on this forum? [migrated]

On this page Dr. Pierre-Marie Robitaille: On the Validity of Kirchhoff's Law there are the following comments this might enlighten you rationalwiki.org/wiki/Pierre-Marie_Robitaille . There was ...
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2answers
55 views

How to show state functions are perfect differentials, or vice-versa?

Suppose a variable $z$ is a function of two independent variables $x$ and $y$. Now, if z can be expressed in its total differential form as $$dz=Mdx+Ndy$$ Then show that $z$ is a state function iff ...
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ferromagnetic and Curie temperature. Energy question

Is energy absorb and release back when a ferromagnetic material heats and cools passing through the Curie temperature?
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45 views

How do free electrons conduct heat in a metal?

In a metal, how do free electrons conduct heat? Does the specific heat of a metal should be then related to the electrons and not the atom of the metal?
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1answer
43 views

Differential derivation based upon time and space confusion

I have been doing a lot of derivations recently involving heat transfer. I was attempting to derive heat accumulation in a differential element based upon inflow and outflow as well as thermodynamic ...
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1answer
26 views

Methods to solve a vapor pressure equilibrium question with water on the moon? [on hold]

"Imagine a tall column of water on the Moon, maintained at a temperature of 50°C and left to the open vacuum at the top. Up to what depth will the water continue to boil? The Moon's radius is 0.273 ...
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0answers
19 views

COP and input work in a refrigerator [duplicate]

Where can i find a COP and input work requierd in a standard modern refrigerator? I need a sample refrigerator, so that I can calculate the heat disposed to the surrounding and use that to design an ...
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1answer
44 views

Partial derivatives vs total derivatives in thermodynamics

The specific heat of a system is defined as $$C_z = T \left( \frac{\partial S}{\partial T} \right)_{z=\text{const}}$$ Sometimes however, I find the same definition, but with total derivatives ...
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94 views

Reading differential forms

When, usually in text of physics or concerning thermodynamical aspects of chemistry, I find notations such as$$\mathrm{d}f=g\,\mathrm{d}t$$ I always interpretate it as ...
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1answer
42 views

$dU = \sum E_i dp_i + \sum dE_i p_i = TdS - PdV \implies \sum dE_i p_i = - PdV$? [on hold]

This is a formula my professor gave in class, but I'm entirely lost how he arrived at the conclusion (I understand the assumption). Could anyone help me?
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Temperature change in Adiabatic stretching of liquid film

The first law applied to a liquid film is $dU = dQ +2\sigma dA$ where $\sigma$ stands for surface tension. Or $dQ = dU + (-2\sigma) dA \leftrightarrow dQ = dU + PdV$ Now suppose we wish to find ...
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16 views

what is the relation between heat capacity and mixing ratio

I am supposed to derive an expression for the specific heat capacity $c_p$ for air with a water vapour mass mixing ratio of $\mu$. The hint is: (Use the fact that $c_p= (\frac{\partial H}{\partial ...
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2answers
85 views
+50

Why do some substances undergo sublimation while others do not?

This question is indeed lengthy...but please go through the question at least. From the study of kinetic theory I know that for intuitive answers we can associate the states (liquid, solid,gas) with ...
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4answers
91 views

The impatient hot tub owner [on hold]

An impatient man owns a 300 gallon hot tub. He comes home from a hard day of work and sees that his hot tub is currently simmering at 90F. For maximum relaxation, he wants it at 104F. However, the hot ...
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1answer
27 views

Using Steam to lift a mass? [on hold]

I have a task set to create a system to produce the largest values for potential energy, mgh. I am given 1 litre of boiling water and with this use the steam produced to lift the mass of weight ...
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1answer
135 views

Entropy of the cosmological constant and the laws of thermodynamics?

Convention The convention being used is: $ A_{C} = $ The classical variable Premise Consider the following toy-model universe: A universe with a positive cosmological constant. Basic ...
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2answers
57 views

Does shaking a kettle whilst boiling increase the temperature faster than a statically-placed jug?

Water molecules move faster at higher temperatures. Does shaking a boiling kettle whilst it is in the process of boiling water increase the rate of rising temperature ? Is it worthwhile to do so ...
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1answer
41 views

What impact does water vapour have on incoming solar radiation?

About 55% of solar radiation at TOA (ie ~700 w/m^2 at peak) is in the infra red. This compares to about 530 w/m^2 at peak of terrestrial IR. Water vapour acts on this radiation, blocking and ...
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1answer
70 views

Why does time always flow forward?

According to the BBC Earth " Physics says that any event in our day-to-day lives could happen in reverse, at any time".Then why can't we just turn time backwards?
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Can I find equation of state if I have a type of potential?

How can I find equation of state if I have a type of potential? For example, if I want to take into account ion-ion, ion-electron, electron-electron interaction in white dwarfs.
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2answers
53 views

Why is the net entropy change of an irreversible engine positive?

In a Carnot engine the net entropy changein a cycle is zero. But in an irreversible engine operating between two temperatures the net entropy change in a cycle is positive. As I have understood, this ...
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1answer
98 views

Number theoretic loophole allows alternative definition of entropy?

A bit about the post I apologize for the title. I know it sounds crazy but I could not think of an alternative one which was relevant. I know this is "wild idea" but please read the entire post. ...
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2answers
96 views

Why is entropy defined as a discrete sum over all microstates in classical case?

I'm reading about statistical definition of entropy, which says $$S=-k_B\sum_ip_i\ln p_i,\tag1$$ where $k_B$ is Boltzmann's constant, and $p_i$ is probability of $i$th state to be occupied. But in ...
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2answers
99 views

Doesn't the success of statistical physics seem somewhat unreasonable?

It seems to me a rather big coincidence that statistical physics works so well. I can see how consistent macroscopic observations can occur just because the microstates that give rise to that ...
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50 views

If a system has an internal energy equal to 0, does this mean it doesn't exist?

Enthalpy is a measure of energy in a thermodynamic system: It includes the internal energy, which is the energy required to create > a system, and the amount of energy required to make room for it ...
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4answers
46 views

how is a pendulum clock's time and the time period of the pendulum in it related? [closed]

I'm working out how much time a pendulum clock will gain or loose due to change of the length of the pendulum due to temperature. so far I've got, new time period, $$T_2=T_1(1+\frac12\alpha\Delta T)$$ ...
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31 views

Have we found a resolution to the Loschmidt paradox? [duplicate]

Loschmidt's Paradox (also known as the Reversibility Paradox) claims that it is not possible to deduce an irreversible process from time-symmetric dynamics such as the classic dynamics. This puts the ...