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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Charge diffusion
Considering the following current in flat Minkowski space
$$J^\mu=nu^\mu -\sigma \Delta^{\mu\nu}\partial_\nu \mu,$$ where $n$ and $\sigma$ depend on chemical potential $\mu$:
$$\mu=\mu_0+\varepsilon \...
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A gas absorbs heat $Q$ isobarically
I encountered a question asking "When gas absorbs heat $Q$ isobarically, what will be its work done, change in internal energy and temperature?" The work done is obviously positive, but I ...
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Why is Mayer's relation $c_p - c_V = R$ and not $\frac{1}{2} R$
Let me show you my thought process and let's simplify it to a single atom instead of 1 mole. $k_B$ is double the amount of energy per one degree of freedom of a particular gas per atom (or $\tfrac23$ ...
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How to calculate the capability to heat a gas mixture via light emission that only some of the gas can absorb?
Consider a tank of gas with volume $v$ that's a mixture of gas $A$ (e.g. helium) along with some fraction $x$ of gas $B$ (e.g. nitrogen), at pressure $P$. For the purposes of the example assume $x \ll ...
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Is there a "4th law of Energetics"? How is energy conserved in a stationary flow through a pair of semi-permeable membranes?
I asked this question but got no replies there.
The below longish quote is from Rosenberg's Some Aspects on Brønsted's Energetic Theory. It concerns two chemical species, $A$ and $B$, in a stationary ...
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How the temperature used in second law of thermodynamics and ideal gas law equivalent? [closed]
I was reading Theory and Problems of Thermodynamics by Schaum's Outline series and there the author starts from some axioms (which are the thermodynamic laws, excluding the zeroth and third). Then he ...
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Computation of free energy profile as a function of collective variables
I was trying to understand the following paragraph in Ref 1 about the computation of the free energy profile of collective variables:
While free energy can be expressed as the logarithm of a ...
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How to find warming rate of an irradiated surface?
I am trying to model the warming of a greenhouse for a differential equations project because I'm interested in math and gardening. I was hoping to work it all out myself from some basic ...
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What is the difference between a macrostate and an ensemble?
I'm not entirely sure about the difference between a macrostate and an ensemble, though I think they are different. To me, it seems correct that both terms can be used to refer to a collection of ...
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Why won't hydrogen gas heated via conduction/convection emit a blue light / how can it emit infrared light?
According to the European Space Agency:
Every object with a temperature above absolute zero (that corresponds to 0 K, or -273 degrees C) emits electromagnetic (EM) radiation over virtually all ...
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The average of a continuous value: $\overline{O} = \int O(x) \rho(x) dx$, but coordinate invariant
I am trying to solve a Lagrange multiplier problem for the following equation
$$
L= - \int_{-\infty}^\infty \rho(x) \ln \frac{\rho(x)}{q(x)} dx + \alpha \left( 1- \int_{-\infty}^\infty \rho(x) dx \...
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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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Why is the drop in water pressure caused by air in water? [closed]
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 ...
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Questions on $\Delta S = \frac{q}{T}$
My Thermodynamics book discusses three types of expansions of an ideal gas and the change in entropy $\Delta S$ associated with each expansion, all of which take an ideal gas in a piston from $V$ to $...
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Why can't a reflective barrier raise an object's temperature past a heat source's temperature?
Say I have a 1 $m^2$ source of visible light emitting 1,000W worth of light. This is shining down upon 1 $m^2$ of ground.
If we treat the ground as a blackbody, my understanding is that eventually it'...
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Can someone explain this to me? About reversible computing with finite energy and thermal equilibrium
In Life, The Universe, and Nothing: Life and Death in an Ever-Expanding Universe, they examine the implications of dark energy on the ultimate fate of life.
Then they say this,
It was long thought ...
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Why can't fire heat something hotter than itself, but electromagnetic waves can heat something indefinitely?
Part of my question on Can a low-energy source/object heat a higher-energy object via radiative heat transfer? asked if a 100W lightbulb could heat a blackbody in a vacuum indefinitely, presuming ...
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Reconciling the notions of $\Delta G$ as a criterion of spontaniety and as the maximum non-expansion work
For a closed system that stays at constant temperature and pressure, regulated by the envrionment acting as a reservoir, it can be proven that
$$\Delta S^\text{Univ} \geq 0 \iff 0 \geq \Delta G,$$
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Solution of gases (i. e. carbon dioxide) in water
This question is related to my former question "Dissolution of Carbon Dioxide in water" and thanks for previous replies. It looks not so easy, so allow me to restate it (*)
Is there a ...
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Balancing forces in a movable piston
I need to balance forces on the "plate" of a piston situated in a closed container of a given spring constant k and area A with a compression x. It is also given that the initial pressure ...
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Why is superheated steam a thermal insulator?
I have read on the wikipedia article on superheated steam that superheated steam has the same thermal conductivity as the air and so it is athermal insulator.
Does anybody knows the reason for this?
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$dq_{rev}$ and $dq$, which one is larger? [closed]
Im learning about entropy and some concepts makes me confusing.
For a reversible and irreversible process with a same initial state and final state, it is said that entropy change of a system is ...
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What is temperature in the classical entropy definition?
Entropy change for a system is defined classically as:
$$dS=\frac{\delta Q_{rev}}{T}$$
where $\delta Q_{rev}$ is infinitesimal reversible heat that flows in a system.
I don't understand whether $T$ ...
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Can a low-energy source/object heat a higher-energy object via radiative heat transfer?
Say we have a blackbody sphere in a perfect vacuum with surface area of $1 m^2$ at temperature 5.1205 C = 278.2705 K. Let's say inside the sphere it has its own energy source that is outputting enough ...
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Why is the ideal gas law said to be classical when it assumes quantized energy states? [duplicate]
We are told in my thermodynamics class that the ideal gas law is a classical law that follows from classical mechanics. However, when we derived it as follows, we computed the partition function $Z_1$ ...
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Why isn't heat capacity defined as $(\frac{d\tau}{dQ})_V$ instead? [closed]
In my thermo notes, $C_V$ is defined in words to be the heat needed to change the temperature of the system. Intuitively, this definition "adds heat" and "measures change in temperature....
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