# Questions tagged [thermodynamics]

Covers the study of (primarily homogeneous) macroscopic systems from a heat/energy/entropy point of view. Consider also using the tag: [statistical-mechanics].

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### At what size of matter does the second law of thermodynamics breakdown?

I'm in high school and I was studying some topics related to heat transfer. While studying, I was curious about why heat strictly flowed from a higher temperature (more energy) to a lower temperature (...
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### Is the increase in the internal energy of an ideal gas equivalent to an increase in thermal energy?

ΔU = Q - W Q: Heat received by the gas from the surroundings (positive if received, negative if given to the surroundings) W: Work done by the gas on the surroundings (positive if done on the ...
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### Where do we get $\Delta U = nC_vT$ from? [duplicate]

The change in internal energy at constant volume is $Q=nC_v\Delta T$ Why does the same equation apply for constant pressure?
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### Thermodynamic work and potential functions

I was reading about the maximum thermodynamic work of a system (Z) that is going to equilibrium. $$dZ = dU + p_0 + T_0dS$$ I then came across the thermodynamic potential ...
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### Is the 2nd law a reason for the irreversibility of natural processes or a consequence of it?

I have been introduced to chemical engineering thermodynamics due to my academic background. I had learnt about internal energy, entropy etc and applied the equations to various scenarios of practical ...
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### Entropy change of an isolated system consisting of two thermally conductive blocks of equal isochoric heat capacity at different temperatures

A classic example considered in most introductory treatments of elementary thermodynamics consists of two thermally conductive (e.g., metal) blocks placed in thermal contact. In particular, I find ...
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### Relating specific heat capacity with the rate of cooling

By Newton’s law of cooling, the rate of heat loss (cooling) is directly proportional to the difference in the temperatures between the body and its environment. On the other hand, Specific heat ...
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### Measurability of the energy difference of two states with different mole numbers

In H.B. Callen's thermodynamics (2nd ed. p. 18), after expaining why "the methods of mechanics permit us to measure the energy difference of any two states with equal mole numbers", the ...
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1 vote
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### If I'm inside water, is the amount of heat energy I can receive capped because water can't go above 100°C?

I just learned about double-boiling, where instead of putting a pot directly on the flame stove (where it can get too hot), you put a big tub of water on the flame, and put the pot in the tub of water....
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### What do we mean when we say the CMB has a temperature and how do we measure it?

I have read this: An object without any internal degrees of freedom, like a single photon, can't really have a temperature. But an ensemble of photons can have a temperature. If you put an ensemble ...
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### Does the expansion of the universe cause the universe reach maximum entropy faster than a non expanding universe?

I've seen Does an expanding universe cool down? So I understand an expanding universe cools down, my question is, does an expanding universe reach maximum entropy faster than a non-expanding universe? ...
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### Thermodynamic diagrams in Hamiltonian mechanics

If we compare the fundamental thermodynamic relation $(1)$ and the Hamilton's principal function $(2)$, than we have two practically identical equations: $$dU=TdS-pdV \tag1$$ $$dS=pdq-Hdt\tag 2$$ In ...
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### Should I hold a baby formula bottle to cool it down faster?

This is an interesting and somewhat surprising physics problem - holding a hot object in your hand will cool it down faster, even if the air around is colder. I guess that 90% of people would be ...
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### What are good introductory books for contact geometry in non-equilibrium thermo?

As far as I can understand, Mrugala's paper on the geometry of thermodynamic processes covers introductory prerequisites for the contact formalism applied to thermodynamics, however, I know there's a ...
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### Landau and Lifshitz Principles of Statistical Mechanics

I've been reading Landau and Lifshitz book on Statistical Mechanicals and some aspects about how they lay out the principles has me a little confused. Let us now consider a macroscopic body or system ...
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### Unitary Evolution and the Second Law of Thermodynamics [duplicate]

Apologies for the long question. This problem has been mentioned multiple times on this platform, with no real resolution, in my opinion. So I'd like to gather all my thoughts below with hopes of ...
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### Estimating Heat transfering by measuring [closed]

Consider the setup with closed chamber with two flat metal objects with know dimensions. The first object can be heated or cooled by peltier module and the second one is placed on top of the first one....
1 vote
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### Contribution of rotational mode in ideal gas law

The ideal gas law is very accurate for an $N_2$ gas when the temperature is around 300K and the pressure is around 1atm. At these conditions, $N_2$'s compressibility factor is 0.997, which means that ...
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### Why can photon be treated like gas?

In Cosmology, especially when studying Cosmic Dynamic, sometime we will treat photons as gas to calculate its pressure, but according to my understanding, photon and gas are nothing alike. Why can ...
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### Net particle number density for relativistic particles at finite chemical potential (tricky integral)

Question: How does one show that the chemical potential of relativistic fermions is negligible at high energies? In particular, I would like to show that the difference between the particle density $n$...
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