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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Why has warm air a higher water saturation than cold air?

I've wondered about that for a while but all I read is commonly just "Warm/hot air has a higher energy so when it hits the surface of a liquid, it has a higher probability to transfer energy, ...
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Small deviations from equilibrium and the grand canonical ensemble

I am referring to and quoting "Equilibrium and Non-Equilibrium Statistical Thermodynamics", by Michel Le Bellac. In equation (2.75) the grand partition function is: $$ Q = Tr\exp(-\beta H + \...
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Spectral radiance and energy of oscillation

The outgoing long wave IR spectral radiance graph by wavelength shows the spectral radiance of IR increasing as wavelength goes from 5 microns to 10 microns but the energy of oscillation goes down ...
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Heating a gas in an insulating cylinder

Let's say I have an ideal gas in a cylinder with adiabatic walls. This cylinder has a piston (thermally insulating as well) in between dividing the volume in half. If I have a heating coil in one ...
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How effective and safe is it to improve home air conditioning efficiency by spraying the sides of the condenser unit with water from my garden hose?

I am trying to take advantage of evaporative cooling and tried spraying the AC condenser unit's wall with water (probably the heat exchanger part). The hot air that normally comes upward from the ...
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Why does the room with less temperature involve more atoms in the given example?

Suppose we have two rooms A and B that are the same size and connected by an open doorway, so the air has the same pressure and volume in both rooms. This means that $P_AV_A = P_BV_B$ and $n_AT_A = ...
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Contradictory mean atmospheric pressure value

In Schröder's Thermal Physics: "$1$ atm = $1.013 \times 10^5$ Pa And under the solutions of one of the questions in the same textbook: One atmosphere is $9.80665 \times 10^4$ Pa Why do they ...
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Theoretical proof of Clausius inequality (Fermi)

I found a similar question but I could not solve my doubt. So, if you consider this question to be a double, I am sorry. Consider a system $S$ that undergoes a cyclic transformation and the $n$ ...
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What gets warmer faster: icewater or just ice?

Revised Question (07/07/20 14:00 UTC) Working off of a suggestion by @GiorgioP: "Would it be fair to say that your question is about the difference of melting behavior of ice if surrounded by ...
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How is the free energy of Kosterlitz-Thouless transition smooth yet non-analytic?

Here is an answer by @tparker which makes the following remark "... a Kosterlitz-Thouless transition, at which the free energy density is smooth but non-analytic..." The expression for the ...
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Can a material absorb latent heat without a phase change? [closed]

Defining latent heat capacity as heat absorbed without a rise in temperature, is there any known material that has a capacity to absorb latent heat without a phase change? If this is not possible then ...
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Need help with heat exchanger requirements

Disclaimer: Not an engineer I need some help determining the required performance from a heat exchanger for a pseudo-instant hot water system on a boat. Using a heat exchanger, and a reserve of hot ...
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The degree of freedom in kinetic gas theory

What is the degree of freedom in kinetic gas theory? How can I determine how much degree of freedom some molecule has?
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Is the volume change during a phase change quasistatic?

I am trying to justify the use of $dS=\frac{dQ}{T}$ for the change in entropy instead of the more generic $dS=\frac{dU}{T}$. According to Schroeder, in order to do so, one has to confirm that the ...
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23 views

Internal Energy of Molecules

How can I determine the internal energy of a number of a certain molecules at a given temperature? If I have a number of a certain molecule, how can I calculate it's internal energy?
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Is number density uniform ($n = N/V$) in equilibrium for Boltzmann distribution?

It is often said in the physics papers or textbooks that in equilibrium if there is no external potential then number density is uniform $n = N/V$, where $N$ is number of particles, $V$ is volume. I ...
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Laplace correction for speed of sound in air

In the Laplace corrrection for velocity of sound, the bulk modulus is replaced by gamma×Pressure. $(\gamma=c_p/c_v)$ In its derivation $$PV^{\gamma} =\text{CONSTANT} $$ is used. And the reason given ...
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Why does the resistance of a tungsten filament level of at a certain temperature?

I have tungsten filament. When I apply a voltage and measure the current and calculate the resistance. I can see that the resistance of the filament increases over time (due to the increasing ...
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Is it possible to derive the canonical ensemble without the microcanonical one?

I'm trying to understand if the microcanonical entropy $S_{mc}=\log(\Omega)$ with $\Omega=\int\frac{d\vec{z}}{h^{3N}N!}\theta(E-H(\vec{z}))$ is somewhat more "fundamental" than the canonical ...
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Entropy of photons in the Sun / Earth system - Do infrared photons have higher entropy than ultraviolet/visible photons?

The entropy of a photon gas in equilibrium (emitting e.g., black-body radiation; BB) is $S \propto V \cdot T^3$ where $V$ is the volume and $T$ is the temperature of the gas [see https://en.wikipedia....
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Why is the work done in reversible process greater than work done in irreversible process?

I have read in my textbook that maximum work is done by gas in a reversible expansion, but I do not know the reason behind it. Also is work done by gas maximum in reversible compression also?
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Does data compression require energy? [closed]

Suppose I have a $C=1TB$ hard drive $H$, filled to the brim with English text. I'd like to compress this. Suppose the hard drive consists (abstractly) of zeros and ones, and that the number of ones in ...
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Temperature dependence of viscosity in liquids

I have been going through the literature on viscosity of liquids and their temperature dependence. The most commonly used forms of temperature dependencies are Arrhenius (eq. 1) and Vogel-Fulcher-...
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The correction of the lattice heat capacity

Some articles extracted the magnetic and electron contribution from the heat capacity by subtracting another isostructure compound (e.g. $C_p(\rm{CeRhIn}_5)-C_p(\rm{LaRhIn}_5)$). Are there any ...
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Van der waals gas free expansion from $V_1$ to $V_2$, [closed]

I have a Van der waals gas which freely expands form vol1 $V_1$ to vol2 $V_2$, the free energy of a Van der waals gas is given to me by: $$F=-Nk_BT[ln(n_Q(V-Nb)/N)+1]-(N^2a)/v$$ while $$n_Q=\sqrt(...
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HEAT liberated in mechanical processes [closed]

Can we calculate heat liberated without changing our frame, in the situation of sand [from rest] falling on a moving conveyer belt maintained at steady speed. And in question in picture, how is that ...
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Heat transfer from one body to another by radiation

How can I calculate the temperature of a metal if at a distance of 1mm there is another heated metal that is at 3000K? Note: the system works in vacuum
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“Cooling down” a column thermometer

Typical medical thermometers based on a capillary mercury or fluid column expansion usually require employing centrifugal/acceleration methods to drive the fluid back to the bulb after performing a ...
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Literature to learn thermodynamics coming from a statistical physics background

I would like to read a book which rigorously defines what in applied thermodynamics is called "heat" and gives a proper derivation of the laws of thermodynamics from quantum statistics and ...
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Statistical definition of heat capacity

In Wikipedia there is this engineering definition of heat capacity The heat capacity of an object, denoted by C, is the limit $$ C=\lim_{\Delta T\rightarrow 0}\frac{\Delta Q}{\Delta T}$$ I'm very ...
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How much energy is required to boil and maintain boiling water temperature for a set time period?

I am trying to calculate the amount of energy required to bring 1 litre of water up to boil (from 20 degrees C to 100 degrees C) and to maintain the water temperature at 100 degrees C for a period of ...
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Meaning of the Planck Temperature

I don't understand what makes the Planck Temperature the "absolute hot". To my understanding Temperature is just a measure of the kinetic energy of the particles, so is the Planck ...
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Materials to Insulate Against Convection, But Not Radiation

Are there any materials which could effectively insulate against convection (and/or conduction), that don't insulate against radiation? Specifically, I want to make a water-heater that uses solar ...
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Do people work on improving battery efficiency by increasing entropy difference?

I have been reading a Daniel Schroeder's book called "An introduction to Thermal physics", and after having completed first couple of paragraphs of "Free energy as available work" (...
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Thermal Coefficients as second order derivatives of thermodynamic potentials

Can we represent the thermal coefficients as second-order derivatives of any of the thermodynamic potentials?
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If I saw two gears turning in front of me, how would I know which of the two has its own turn? [closed]

If I saw two gears turning in front of me, how would I know which of the two has its own turn? In other words, one gear rotates another static gear. How do I know which gear has its own movement?
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Temperature dependent heat capacity and entropy

this problem is often presented as a simple demonstration of relationship between the heat capacity at constant volume $C_V$ and entropy $S$. Let's say the heat capacity $C_V$ is equal to $a T + b T^3$...
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Diffusion of gases of different temperature [closed]

Let a box be divided into two parts by a partition. Let each part be filled in by the same gas in equal concentrations but different temperatures. Let the gases start diffusing through a hole in the ...
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In an ideal gas, is the pressure dependent on the mass of the molecules?

If you take the ideal gas law and substitute $\dfrac mM$, where $m$ is mass of the particles and $M$ is molecular weight, you can derive $D = \dfrac{MP}{RT}$ with algebraic manipulation, where $D$ is ...
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Working of a desert cooler?

Does level of water have any effect of the capacity of cooling in a desert cooler ? The fan rotate with a constant angular velocity so how and why does the water level effect the coolness capacity ...
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Going from 1st state to 2nd through irreversible isothermal expansion and coming back to the initial state through compression is not possible. How [closed]

My teacher was teaching me that how work done in isothermal reversible expansion is greater than irreversible expansion and also work done in isothermal irreversible compression is greater than that ...
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A constraint equation between two systems in thermodynamic equilibrium

In several introductory statistical mechanics books/notes I have seen, the idea of equilibrium is introduced by asserting the existence of a constraint equation between the properties of two systems, ...
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Heat loss calculation and Energy Balance

The image shows the CAD model of the annealing zone in a galvanization simulator. The zone is electrically heated with a AC current of 5597A at 2.09V. This whole zone is surrounded by insulating ...
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Derivative of internal energy with respect to pressure at a constant volume

I need to obtain the derivative of internal energy $U$ w.r.t. pressure $p$ at a constant volume $V$. Realizing that $\mathrm{d} U = T \mathrm{d} S - p \mathrm{d} V$, I rewrite $$ \left( \frac{\partial ...
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What is an arraylike structure of thermoacoustic sources?

In this article there is the following text: In the linear regime, a laser beam incident at the boundary is exponentially attenuated by the medium. 10,11 The water medium absorbs the optical energy, ...
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Why is not both sides of a fan equally effective? [duplicate]

I have a fan on my desktop. I started to wondering if it would not be just as effective if I flipped it 180 degrees. Since all the wind that comes out of the front has to be sucked in from behind, ...
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Is it dangerous to put a pressure cooker under cold water after cooking?

After cooking using a pressure cooker, it usually takes a while for the pressure to be released and for the cooker to be opened. However when I think the food may have been slightly overcooked, I take ...
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Physical interpretation of $pV= 0$ for Einstein Crystal Model

There is a difficulty with the pressure of the Einstein crystal model. The model does not include any simple way to evaluate the derivative in Eq. (28.2-7e). We might try to evaluate the pressure by ...
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Examples of processes that are reversible isentropic but not adiabatic?

Since $ds=\frac{dq_{rev}}{T}$ for reversible processes it seems we can have reversible isentropic processes that are not adiabatic provided the temperature changes in such way that the sum of $\frac{...
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A guess at the derivation of the entropy formula in ideal gas [closed]

In my high school physics textbook, I found that they define entropy change in a reversible isothermal process as: $$\Delta S = \frac{Q}{T}$$ where Q is the heat added to or removed from the system ...

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