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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Does Maxwell's demon include the knowledge of the experimenter?
We know Leo Szilard was right when he said the demon would need to expend energy to know which molecules are hot or cold, and there has been experiments that have converted information to energy using ...
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Why doesn't the accretion of ice, cause the ice to melt?
I was reading about the accretion of ice which describes the rate at which the ice layer above a lake thickens. It said that in order for the water just below the ice to solidify,heat had to be ...
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Stationary ensemble and intuitive understanding as to how a statistical ensemble is represented via probability density in phase space
In Wikipedia, in the article about the statistical ensemble, it is said that in classical mechanics (thermodynamics and statistical mechanics) the ensemble is represented via the probability density ...
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Why does the depletion region in a reverse biased diode grow?
From what I understand, at the pn-junction of a diode, electrons diffuse from the n-region into the p-region until the resulting electric field grows large enough to stop any further flow of electrons....
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Self-calculated radiative thermal conductivity does not match literature values
According to various sources (nicely collected in Gardons review) the radiant heat flux within an opaque material (like fused silica) may, in the steady state limit, be expressed with a thermal ...
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How to obtain Non-Equilibrium (NE) Statistical Associating Fluid Theory (SAFT) expressions starting from equilibrium SAFT expressions?
I'm interested in applying Non-equilibrium Thermodynamics for Glassy Polymer (NET-GP) [1] framework to Statistical Associating Fluid Theory (SAFT) variations (e.g PC-SAFT [2]).
In short, the main NE→...
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What is BPS state?
I am preparing a presentation about black holes thermodynamics in string theory. Both in polchinski and in many famous articles there is a discussion about BPS and I am not able to understand why it ...
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Has the entropy of a single photon ever been measured?
Light fields have entropy, as already discussed by Planck.
As a consequence, photons have entropy.
The entropy of single photons is some factor of order unity times the Boltzmann constant. The topic ...
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Chapman–Enskog theory and a Noether's invariant of energy?
So in this answer:
Folks figured out thermodynamics before statistical mechanics. In particular, we had thermometers. People measured the "hotness" of stuff by looking at the height of a ...
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Does order of adding hot/cold additions affect temperature of beverage? [duplicate]
I make my coffees in the morning by brewing a shot of espresso (hot) then adding some water (hot) and then adding some milk (cold).
If I add the milk (cold) first then add the water (hot), would that ...
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The universal value of Boltzmann constant?
So I'm quite confused about Boltzmann's constant $k_B$ being fundamental. From here:
... the Boltzmann constant. Its value is well known but even if its value were 10 times bigger or if it were ...
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What might get me to the lowest temperature with liquid water?
I'd like to experiment with freeze drying food but the only equipment I own, is a vacuum pump+chamber and an old freezer I wouldn't mind drilling to run a vacuum pipe inside.
However an important ...
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Determining the pressure after an adiabatic compression
(Please avoid explaining it with calculus)
I need to determine the pressure of air after an adiabatic compression. I have been given a low starting temperature T1 and a high final temperature T2 and ...
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Confusion about Boltzmann distribution
It is well-known that the Boltzmann distribution is given by $p\propto e^{-E/kT}$, where $E$ refers to the energy.
A standard textbook problem is to find the pressure variation in a rotating cylinder ...
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Pressure cooker becomes pressurized again after closing and opening?
While cooking food in my pressure cooker today, I pulled the whistle using my spatula to let the steam off before I opened it to check on how well cooked the food was. Before, I opened the pressure ...
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Can Heat Change the internal potential energy of a system
What I know is that heat supplying heat increases average kinetic energy of molecules, but does it has any affect on potential energy of system. I have a intution that supplying heat might decrease ...
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Why black hole erase information
It is usually said that according to the no hair theorem, black holes erase the information enter them which reduce the entropy and imply the so called "information paradox".
The problem is ...
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Why does a piston oscillate at a much lower frequency than a standing wave within a tube?
I have a thermoacoustic engine, with a stack producing sound waves - the piston is attached to the open end of the tube, but why does it oscillate at a much lower frequency than the sound wave itself. ...
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Force to balance the force by atmosphere
In the container containing water,let us consider the uppermost surface which is contact with the air. The force by atmosphere $P_oA$ is acting on the upper most surface. If we assume the water to be ...
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Entropy change for a real gas via Peng-Robinsons EOS
Consider a process with inlet conditions ~300K,~50Bar and outlet conditions ~350K,~150Bar. Entropy departures as per Peng-Robinsons EOS. I am evaluating the entropy change via the following:
∆𝐒 = 𝑺𝒅...
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Maximum Entropy Principle with inequality constraints
It is well known that, maximizing the entropy of the joint distribution $P(x_1,...,x_n)$ of a random vector $(X_1,...,X_n)$ subject to equality constraints for the mean vector ($\mu$) and the variance ...
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What is the difference between flow work and kinetic energy in thermodynamics?
I'm having a hard time understanding what the difference between flow energy and kinetic energy in a fluid that moves. My book gives me the following equation for mechanical energy of flowing fluid:
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Is the value $k \ln 2$ the largest or the smallest entropy that a single particle can carry? [closed]
Sorry, but I lost the reference of the author telling this.
Is $k \ln 2$ the largest or the smallest entropy that a single particle can carry?
And why is this so?
EDIT:
It was a paper from the 1970s.
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Derive the dimensionless Gibbs free energy equation [closed]
I'm having trouble deriving the Gibbs free energy equation:
$$ G = \sum_i n_i \left(g_i^0(T) + RT\ln P_i\right),$$
then,
$$\dfrac{G}{RT} = \sum_i n_i\left[\dfrac{g_i^0(T)}{RT} + \ln P + \ln\left(\...
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Maxwell Boltzmann speed distribution: why isn't speed element integrated when converting from velocity distribution? [duplicate]
Maxwell Boltzmann velocity distribution is given by $$f_{\vec v}(v_x,v_y,v_z)=A^{3/2}\exp{[B(v_{x}^{2}+v_{y}^{2}+v_{z}^{2})]}$$
To convert the velocity distribution into speed distribution, spherical ...
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Presure vs Energy density
I'm having trouble to intepretate a graph where in the y-axis there is Pressure ( $P \equiv=-\frac{\partial E}{\partial V}$) and on the x-axis energy density ( $\varepsilon\equiv$ E/V ). If there is a ...
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Is the universe getting hotter? Brighter?
Due to their fusion processes every star is radiating massive amounts of photons and (to a lesser extent) neutrinos. Are all of these getting absorbed in matter over time, warming it, or is the total ...
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Is it possible to split up air into its parts by something like centrifuging? [duplicate]
Is it possible to centrifuge cases to split them up into their compounds (at least temporarily)?
For instance, the air is composed of 78% nitrogen, 21% oxygen, 0.9% argon, and other gases. Under what ...
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Entropy balance of surroundings in open systems
In my text book, "Chemical, Biochemical, and Engineering Thermodynamics" by Sandler.
The entropy balance equation for an open system is defined as,
$$\frac{dS}{dt}_{sys} = \sum_k M_kS_k + \...
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Difference between two Enthalphy equations
I am revising thermodynamics and in the textbook, the enthalpy equations are stated in two forms.
"H=U+pV" and "h=u+pv". What is the difference between the two equations.
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Does the Sun increase entropy?
The Sun generates heat via fusion. The heat from this reaction gets distributed around the solar system and beyond. This process of spewing heat and radiation all over the place doesn't immediately ...
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Is it possible to drive an air cylinder with ignited hydrogen/oxygen gas mixture from fuel cell? [closed]
Summary:
I want to build a linear actuator that has a very fast actuating speed but fits in a very small space. Is igniting hydrogen/oxygen produced from an electrolysis fuel cell in a combustion ...
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What is the correct $pV$ diagram for gas expanding inside sealed cylinder covered with piston?
I am not sure about the correct $pV$ diagram for the isobaric process of gas expanding inside a sealed cylinder covered with a piston when it is heated with candle. The best I can come up is
The zig-...
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Is entropy in the third law of thermodynamics a continuous quantity?
In the third law of thermodynamics, entropy goes to zero or to a constant value at vanishing absolute temperature. The change of entropy also goes to zero.
The third law is valid in the thermodynamic ...
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Focusing blackbody light simulation
As an honest citizen, I do not intend to violate the laws of thermodynamics by concentrating the light emitted by a blackbody on a smaller area. However by playing with this wonderful 2d ray online ...
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How to calculate the total entropy of dS black holes?
In several articles where the thermodynamics of dS black holes have been investigated, the entropy part of the model or the total entropy has been analyzed based on the entropy of the black hole ...
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What exactly is history when we talk about a 'state variable'?
'state variable' - its value depends only on the given state of the system not on history i.e. not the 'path' taken to arrive at that state
While my book does try to explain what 'history' is, it ...
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Why does ice on my car's windshield melt when it's below zero degrees Fahrenheit?
This morning I looked outside at my car and windows were covered in ice. The temperature this morning was -7F. A couple of hours later now the temperature is 0F, yet everything on the car is shiny and ...
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Is there entropic force in a black hole?
A black hole is regarded as a thermodynamic system that has entropy. Its horizon has a temperature and corresponds to a macroscopic system, thus occupying a large number of states. In this perspective,...
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Is heat transfer and work done per unit mass path-independent since it can be expressed in terms of intensive thermodynamic properties of a system?
The argument given for $du = Tds-Pdv$ being applicable to irreversible processes too (even though it was derived using dQ = TdS for a reversible process, from Clausius' inequality. For a non ...
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Work done in expanding a gas
Let's suppose a monoatomic gas of $n$ moles has been expanded from $V_1$ to $V_2$ volume keeping pressure constant. Now from the ideal gas law,we have $PV=nRT$. Taking differentials of both sides,we ...
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ADM Formalism in Anti-de Sitter
While there different ways of defining energy in anti-de Sitter spacetimes in GR (cf. for example arXiv:2209.09031), I never see anyone discussing the ADM formalism in AdS. Does anybody know why that ...
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Why does heat engine efficiency use absolute zero rather than thermal differential?
Carnot's theorem calculates efficiency of a heat engine versus absolute zero. I read the question
Why can Carnot efficiency only be 100% at absolute zero?
But I don't feel it addresses it precisely.
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How to derive Dalton's law of partial pressure for a non-ideal gas?
According to dalton's law,
$$p_i = p_°X_i$$
Where $p_°$ is total pressure of gas mixture and $X_i$ is the mole fraction of the $i^{th}$ component of mixture. This is very easy to derive for an ideal ...
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How can I derive the second law of thermodynamics from Newton's second law of motion? [duplicate]
Do you know of an elementary proof for the second law of thermodynamics, for example, from the Newton laws or perhaps some particular model in which it is equivalent/reduces to it?
My naive concept of ...
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Does a material’s colour affect it’s infrared radiation absorption independent of affecting its visible light absorption?
If you compare 2 metal blocks, one black and one white, the independent variable you have changed is the interaction the outer surface has with (at least) visible light, hence the colour difference. ...
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Holding things constant in Statistical Physics for differentiation
I just want to know if the following is correct:
If one wants to verify e.g. the Maxwell relation for the ideal gas $$\left(\frac{\partial T}{\partial V}\right)_{S,N}=- \left(\frac{\partial p}{\...
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Does condensation depend on partial or total pressure exceeding vapour pressure?
In an answer here, by Dr Kim Aaron, he describes a hypothetical scenario in which there's a piston cylinder system with water. A vacuum pump then sucks out the air. Water evaporates until the pressure ...
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Why does hot water in a hot flask later cool? [duplicate]
What make hot water cool in thermos flask since it doesn’t release energy?
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Why doesn't this buoyant free energy device work?
Okay so I've seen a few of these but the setup here is a bit different.
Suppose we set up an electrolysis plant at the bottom of the ocean and for some constant energy cost $E_1$, we can get a bunch ...
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