# 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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### Are calories an appropriate measurement of energy for biological systems? [closed]

According to this source, a calorie is an inappropriate unit to quantify the energy contained in food because a "calorie is heat energy" and "humans don't absorb photons" but ...
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### Friedmann fluid equation in the non-relativistic case

The Friedmann fluid equation I am referring to is: $$a\frac{d\rho}{da} = -3(\rho+P) .$$ In the non-relativistic (low temperature) case for an ideal gas universe (representing matter), I know that the ...
1 vote
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### Do neutrons have a higher entropy than protons?

Since free neutrons want to undergo beta decay into a proton while protons are relatively stable does that mean that neutrons have higher entropy than protons?
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### $q$-potential in grand canonical ensemble

I was recently going through R.K. Pathria's Grand canonical ensemble chapter and found the following section confusing under physical significance of statistical quantities. The author mentions; To ...
1 vote
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### What is the relationship between Clausius Inequality and 2nd Law?

I am confused about the application of the 2nd Law for reversible and irreversible processes and cycles. I want to know how the Clausius principle, the Kelvin-Planck statement, and the Clausius ...
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1 vote
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### Thermal Smearing in Josephson Junction

I'm basically trying to simulate a josephson junction at a particular temperature. As per some of the plots I could find, the rise in temperature leads to a rounding of the I - V curve. I was ...
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### Is there a practical distinction between functions of state and functionals in thermodynamics?

In thermodynamics, and more precisely when talking about continuous systems, some sources [1, 2] introduce functionals of state: $$F[s(x), \dots]:=\int_VdV(x)f(s(x),\dots,x)$$ In order to derive ...
1 vote
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### How fast does a gas expand in vacuum?

A gas is initially confined to a small portion of an empty container. At time $t=0$ gas is allowed to expand to homogeneously occupy the container after some time $t$. What is the time $t$? This ...
1 vote
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### What is the actual meaning of $dx$ in $W=-F.dx$, in work in thermodynamics?

what I want to ask is that the $dx$ in that formula is the displacement of piston or the displacement of the center of mass of the gas. also is there any situation where this clarity is useful.
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### Heat exchange speed of two liquids separately vs their mixture

I'm quite oblivious about basic high school physics, so pardon my misuse of terms and inability to google the answer. I want to solve a puzzle that I face in my daily routine. Suppose I want to make a ...
1 vote
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### Radiation power emmited by a material with two different temperatures [closed]

Let's consider a cylindrical sample of a solid material surrounded by air. From $0 \leq r \leq r_1$ the temperature of the material is $T_1$ and from $r_1 < r \leq R$, $T=T_0$ which is also the ...
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### Why vacuum does not have absolute zero temperature? [duplicate]

Extrapolation of P vs. T graph gives absolute zero or 0K. Does that mean that if we achieve perfect vacuum, we can have absolute zero? If not why? Let us assume a perfect vacuumn space where there are ...
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### What is the value of the ideal gas constant in J/(mol*°C)? [duplicate]

I've seen in some sites that it is the same as in J/(mol*K), is that true? $8.314 \frac{J}{mol×K}=8.314 \frac{J}{mol×°C}$
1 vote
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### Determining Critical Temperature of Oxygen from Six $p$-$V$ Diagrams [closed]

So the question is to plot six $p$-$V$ curves for oxygen at various temperatures ranging from 80 K to 170 K, using the Van der Waals equation. Having done that, the next part asks to estimate the ...
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### Would a Particle being attracted to a particle that is repulsed by it break the laws of thermodynamics? [closed]

Working on an idea for a magic system in my writing but I want to know what would actually happen if this was a thing. Let's say we have particle A and particle B. Particle A is attracted to particle ...
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### Penning trap laser cooling

In the penning trap, I know that there is a quadrupole electric field and a magnetic field. This results in three eigen motions with three eigen frequencies: magnetron freq, modified cyclotron freq, ...
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2k views

### Will a piece of coal burn at the atomic level at room temperature?

If there is a piece of coal in the open air at room temperature, some of the molecules in the surrounding air will have sufficient velocity to oxidize the carbon in the coal. Will the surface of the ...
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