# Questions tagged [thermodynamics]

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

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### Free energy change in reversible/irreversible processes

Yet another follow up to this question, I am struggling to understand the example provided in Chet Miller's answer: An example of this is expansion of an ideal gas in contact with an ideal constant ...
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### Why there is no process that occurs at constant $T$ and $V$ for system in contact with heat bath?

I was reading the Wikipedia page about Helmholtz free energy and there is a sentence I don't get: We see that the total amount of work that can be extracted in an isothermal process is limited by the ...
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### How to boil 40ml of water using a solar panel of 15v and 1amp? [closed]

I am making an application to use in third world countries where there is unlimited sunshine I need to boile a very small amount of water, up to 40ml, using a solar panel that generates 15v and up to ...
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### Can doing positive work in a system add mass to it?

We know that doing work changes the internal energy of a system. If we transfer energy in the form of work to an isolated system, we cause a change, an increase in the internal energy. Work is force ...
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### Difference between Reversible and Irreversible processes in Physics vs. Chemistry

In Physics a reversible process is defined as one in which the system can be returned to its initial conditions via the same path (along the PV Diagram), and every point along the path is an ...
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### Why does thermal equilibrium between two systems $A$ and $C$ imply the constraint $f_{AC}(A1, A2, · · · ; C1, C2, · · ·) = 0$?

I am trying to understand the mathematical formulation of the zeroth law of thermodynamics. I get that if a system A is in equilibrium with a system C and a system B is in equilibrium with the same ...
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### Free energy of a one-dimensional harmonic oscillator

The potential energy of a one-dimensional harmonic potential can be expressed as $U(x)=\frac{1}{2}K(x-x_0)^2$, where $K$ is the force constant and $x_0$ is the equilibrium position. I'm wondering how ...
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### Does Hawking radiation have a statistical physics origin like the usual derivation of Boltzmann factors?

According to Andrew Steane's Thermodynamics chapter 19 on Thermal radiation: "The total emission from a physical object can usefully be separated in two parts: the thermal radiation and the rest. ...
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### How are black-hole evaporations possible?

It is believed that if, $$R \leq \frac {2Gm}{c^2} \; \;\;\;\; (1)$$ is black hole and due to Hawking radiation it losses mass and subsequently when, $$R \geq \frac {2GM}{c^2} \;\;\;\;\;\; (2)$$ ...
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### Normally distributing particle velocities

I'm trying to set up initial conditions for a collection of N particles distributed on the surface of a unit sphere so that they are uniformly distributed in position and their velocities are normally ...
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### Use of enthalpy of vaporisation for evaporation in a actively pumped vacuum

I have a question relating to non-equilibrium thermodynamics: specifically, lets say that I have a liquid being heated in vacuum (like a liquid iron for example that was being actively pumped by a set ...
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### Beyond the energy equipartition, what is the uneven law?

There is a celebrated energy equipartition theorem, it works fine for many systems. But it requires the dense filling of the surface of constant energy. What if there are other conserved quantities, ...
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### Work done by free expansion of gas and the energy of the piston

So this has been bothering me for a while. I know that for a free expansion of a gas, work done by it is zero. However, I have a doubt regarding the kinetic energy gained by a piston during this free ...
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### Second law of thermodynamics and Unitarity of quantum mechanics [duplicate]

From the second law of thermodynamics, we know the entropy must be increasing in an isolated system, such as our Universe. On the other hand, we have quantum mechanics which, I think, somehow tells us ...
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### Is there a difference in the 'quality' of a gas if it's heated by electromagnetic radiation as opposed to conduction/convection?

According to this link, "The wavelength at which the $O_2$ molecule most strongly absorbs light is approximately $145$ nm." According to this link, that's in the ultraviolet range of the ...
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### Helmholtz energy and thermal equilibrium

After asking this question, I am still confused about some facts regarding Helmholtz energy and thermal equilibrium. Based on my understanding so far, for a system in contact with surroundings which ...
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### Heat conduction through hollow cylinder with constant internal and external temperature

Consider a hollow cylinder of inner radius $r_1$ and outer radius $r_2$. The entire surface of the cylinder is kept at constant (but distinct) temperatures along the interior and exterior. I found ...
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### Thermoelectric effect

Hey just learned about this thermoelectric effect in physics class, I was wondering why it is not used more often in the form of a thermoelectric generator in practical industrial applications. Would ...
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### How can we explain expanding gas temperature at the microscopic level?

An insulated piston and cylinder contains an ideal gas. We pull the piston and expand the gas volume inside the cylinder. I understand the temperature drops due to this expansion. But, how can we ...
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### Gas temperature in a constant volume

An insulated container (constant volume, adiabatic) contains an ideal gas. We open the container's hatch for a few seconds and let some particles escape from the container, then we close the hatch. We ...
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### Standard deviation of kinetic energy approaches average kinetic energy

I have a simulated system of lots of particles modeled as circles moving in 2 dimensions. They bounce off each other and off of walls. Momentum and kinetic energy are conserved. I noticed that the ...
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### Change in Free Energy on Approach to Equilibrium in a System with Fixed Volume

Consider a system whose volume and particle number are fixed. The system starts out at temperature $T_0$ and is then put in thermal contact with a reservoir at temperature $T_r \neq T_0$. It is often ...
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### What is the theoretical limit of adiabatic lapse rate as derived in introductory books?

In meteorology, the Earth's atmosphere up to the stratosphere is subject to processes that are, to a good approximation, adiabatic in nature. Based on the state equation of an ideal gas, the adiabatic ...
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### How a thermodynamical system relaxes to equilibrium?

For a system in contact with a reservoir with well-defined constant temperature $T$, its change in Helmholtz energy satisfies the following inequality: $$\Delta F \le -W_{by}$$ where $W_{by}$ denotes ...
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### What is the underlying concept in case of finding pressure inside a balloon kept at some height in atmosphere? [closed]

If we have a balloon containing air at sea level. Is the value of absolute pressure inside the balloon decided by the temperature of the enclosed air or by the height of atmospheric column above it ...
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First time I connect some pipes, then I fill water pressure into the pipeline to 10 kg cm$^{-2}$, but the pressure became 9 kg cm$^{-2}$ on the next day, I think about pressure drop cause fill air in ...