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Questions tagged [ideal-gas]

A gas that behaves as randomly moving, non-interacting molecules. This allows a simplified equation of state.

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Origin of ideal gas fluid dynamics equations including the adiabatic index

I was given a system of equations that supposedly describes the fluid dynamics of an ideal gas. The equations are: $$ \begin{align} &\frac{\rho}{m} = \frac{p}{T} &\text{(ideal gas law)} \\\\ &...
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What exactly is the translational partition function for a single particle system?

I am recently reading Daniel V. Schroeder's book on thermal physics, and I am having trouble with the translational partition function for a single particle. Particularly since he defines the ...
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Helium balloons losing buoyancy in cold environment

I recently conducted an experiment in the mountains (approx 1700m above sea level) using a series of large tethered helium balloons to measure windspeed at different heights. After only a few hours, ...
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Ideal Gas law and Universal gravitational constant

In a hypothetical universe with a different Universal gravitational constant $G$, will the nature of ideal gas change by any means? i.e, will $PV = nRT$ be no longer applicable in that case?
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Has any work been done to describe the transient behaviour of a non-uniform ideal gas in an adiabatic process?

Recently, I've come across a discussion where a person believed classical thermodynamics predicted loss of energy in free expansion. After discussing for a while, I found out that that person made a ...
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Force and massa unit [closed]

why in this question did the question answer only perform the product between area*P to calculate the mass? Question: Answer: Shouldn't the mass be calculated as $m = (P \times A)/g$? Considering ...
Everson Gomes's user avatar
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Why is the number of microstates corresponding to a macrostate even finite for an ideal gas in a box? [duplicate]

I was looking at the Sackur-Tetrode equation which gives an exact formula for the entropy of an ideal gas. I tried to relate it to Boltzmann's famous $$S = k_B \ln(W)$$ where $S$ is the entropy and $W$...
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Diffusion of van der waals gas

the problem is diffusion of non-ideal gas i think, in this situationm the change of internal energy, work, and heat during process is zero because this process is free expansion(diffusion) but, how ...
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Source of Taylor's "equation of state for a perfect gas"

What is the derivation of Taylor's "equation of state for a perfect gas (10)" in his 1941 paper? What does it even mean?
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Dewpoint of a particular place

can dewpoint of a certain room change if I decrease the temperature or increase it? And what factors does RH,Dewpoint and Saturated cloud pressure depends on?
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What is the pressure immediately after compression of air?

Rearranging the gas law equation to Pressure = nRT/V shows that a reduction in volume by 10 should yield a 10x increase in pressure. But compressing air also causes a rise in temperature. Immediately ...
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Why doesn't $\gamma = \frac{5}{3}$ for all adiabatic processes

For monoatomic, ideal gases, $PV^{\frac{5}{3}}$ is constant. I have been told that this does not hold for diatomic, or other non-monoatomic gases. However, I derived the relationship using only the ...
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The correct formulation of temperature resistivity in Drude model

In this link the document uses $F = ma = qE$ to get drift velocity(Eq.9.6,page10), and then to resistivity(Eq.9.8,page10). But the document also said velocity due to temperature is magnitudes larger ...
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Entropy of mixing via partial pressures

I was deriving the equations for calculating the entropy change $\Delta S_M$ of the system where ideal gases are being mixed. The first one utilizes partial pressures via Dalton's law: $$\Delta S_M= \...
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Internal energy of a gas under motion

Suppose, there a gas in a cylinder which itself is placed on a fast moving car, will there be any change in its internal energy due to the motion of the car? Do you think it may gain some kinetic ...
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Derivation of pressure in the kinetic theory of gases

According to Wikipedia, The pressure exerted by the collisions of the N gas particles with the surface can then be found by adding the force contribution of every particle and dividing by the ...
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Discrepancy in the Derivation of Maxwell-Boltzmann Distribution

I am reading Maxwell-Boltzmann distribution for describing the velocities of ideal gas molecules. I went through the PSE question Derivation of the Maxwell-Boltzmann speed distribution and the ...
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The mean kinetic energy of a gas particle

I'm in undergraduate stat mech/thermo. In the context of the Maxwell-Boltzmann distribution, the mean kinetic energy of a gas particle is $\langle KE \rangle = \frac{1}{2}m \langle v^2 \rangle$. I do ...
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Counting Microstates to get the Entropy Generation in Free Expansion of an Ideal Gas

In Elliot and Lira's Introductory Chemical Engineering Thermodynamics on p.134, the authors derive the entropy generated from an ideal gas expanding from a volume V to 2V, by the removal of a ...
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Does the density form of Ideal gas law hold under condition of changing mass?

I'm trying to get a deeper understanding of this particular form of the ideal gas law I have seen. That form is $P=\rho R T$. I believe this form is not valid when mass or volume is changing. Am I ...
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Could compression make gas colder not hotter?

In classical thermodynamics compression always makes gas hotter because of the mechanical work it inputs. However, if the particle density is too high, particles will become degenerate and obey the ...
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Trouble understanding why ideal gas law explains that can of compressed air gets cold when you spray it [duplicate]

I was told that a canister of compressed air gets cold because of the ideal gas law, you are lowering the pressure and since the density of air is the same, the temperature of the can gets cold. I was ...
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Determine the entropy of an ideal bosonic gas

I am struggling with this problem. So we're told that any macroscopic state of a gas can be characterized by microscopic stated of a single particle. We divide the microscopic states into groups. So $...
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Validity of $C_p-C_v = R$

This might be a very novice question but i got confused over derivation of $C_p-C_v = R$ which is derived using $dQ= n C_p dT,$ which is valid only for isobaric process. Thus $C_p-C_v = R$ must also ...
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Why does the temperature of an ideal gas decrease when expanded? [duplicate]

I understand that when an ideal gas is compressed using a piston, the piston does work on the gas and increases the gas's kinetic energy (so temperature). However, I do not understand why a gas is ...
Varshil MVH Pets's user avatar
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When to use multivariable chain rule in thermodynamics?

If I take $U(P,V)$, I can do: $$ \frac{dU}{dT} = \frac{\partial U }{\partial P } \frac{dP}{dT}+\frac{\partial U }{\partial V} \frac{dV}{dT} \tag1$$ But, I see the following used in books, $ dU = ...
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What would be the pressure, temperature and density gradients with altitude of atmosphere with ideal gas?

What would be the pressure, temperature and density gradients with altitude of atmosphere with ideal gas considerations? That is no convection or radiation. Most of the answers I have seen are ...
Rejeev Divakaran's user avatar
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Entropy change due to surroundings?

What is the entropy generated by opening up a vacuum chamber of volume $V$ to the atmosphere? (let's say with some constant ambient pressure $P_{atm}$) I was reading about Joule expansion, but it ...
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Mass balance for gas in a fixed volume

I am trying to generate an equation that describes the mass balance of a gas in a fixed volume. The application is simulating the sweep out time of the cell in a laser-based instrument which measures ...
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Temperature increase in fixed volume due to gas injection

I have a vessel of fixed volume with adiabatic boundary which is initially filled with air at pressure of 1 atm and temperature of 300 K. Now, I inject air from an external source at a fixed flow rate ...
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Modeling of an ideal gas from a Classical Mechanics perspective

Say we have a box with a (large enough) side $L$ in which there is are $N$ indistinguishable particles, each having a speed $\vec{v}_i$. Let us also say these particles don't interact with eachother ...
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Virial Theorem for Gas Particles

My statistical mechanics professor stated the Virial Theorem as \begin{equation} \langle K \rangle = -\frac12 \sum_{i=1}^N \langle \mathbf{F}_i\cdot \mathbf{r}_i\rangle \end{equation} For an ideal gas ...
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What is the internal pressure of a tethered hot air balloon?

This question is for the review portion of a thermodynamics class: A small hot-air balloon has a volume of $15.0 m^3$ and is open at the bottom. The air inside the balloon is at an average ...
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Leaking gas tank

Say we have a rigid tank of nitrogen gas ($N_0$ molecules) at temperature $T$. The tank is in vacuum. If we now punch a small hole on the tank, the gas will leak. Assume the hole is small enough so ...
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Principal of maximum Entropy (Two ideal gases in mechanical contact) [duplicate]

Consider a container with Volume V. The container is seperated by a non-movable, impearable wall, which allows heat flow. Both subvolumes are filled with an ideal gas. We can obtain informations about ...
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What is the most general and accurate real gas equation?

I've been presented in my thermodynamics course with both the ideal gas and Van der Waals state equations for the study of gases, being the latter more accurate in measurement than the first one. ...
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Why can we not describe matter as an ideal gas when the gas is degenerate

When a low mass stars core mostly consists of helium (after years and years of fusion reactions) its thermal pressure decreases and so the core gets denser due to gravitational pressure. Why is it ...
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Justify uniform density of ideal gas at thermal equilbrium

I'm trying to convince myself that an ideal gas in an arbitrarily-shaped, zero-gravity, closed container has uniform density in space at thermal equilibrium, where I define an ideal gas to consist of ...
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Doubt regarding kinetic theory of gases

My school teacher had told me that one of the assumptions of Kinetic Theory of Gases was that the molecules of a given gas were all identical and to be considered as very small elastic spheres. ...
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Validity of the equation $dQ=CdT$ in different cases

I know this question may be too simple so I apologise for that but nonetheless very necessary. In my class we have defined the heat as $$\delta Q=CdT$$ with $C$ the heat capacity, but I'm unsure if it ...
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Would removing all nitrogen from the air cause altitude sickness effects?

The total pressure in the lungs is close to the external pressure of 101kPa, i.e. breathing requires little delta-P. The removal of all nitrogen in the air would not change the 20kPa partial pressure ...
Kevin Kostlan's user avatar
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Why expansion of real gases lead to cooling?

Paul Hewitt writes in his book Expansion of real gases lead to cooling as average translational kinetic energy per molecule decreases. The reason given is: During Expansion molecules collide with ...
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Collision frequency of a 3D object in a container

Might be a silly questions but I had a thought while learning about the collision frequency of gas molecules on a single surface of a container using kinetic theory. For a 3D object in the container, ...
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Find the ideal gas law from the internal energy [closed]

I'm looking for a way on how to obtain the ideal gas law $PV=nRT$ by being given the internal energy $$U=U(S,V)=\alpha N k_b \left(\frac NV\right)^{2/3} e^{2S/(3Nk_b)}$$ I can find the pressure and ...
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What's happening in this approximation for the equation of state of an ideal gas of bosons

The way we arrived at the equation of state for an ideal fermion gas was to approximate the right handside of $$\beta PV=\sum_{\vec{p}}\log{(1+fe^{-\beta\frac{p^2}{2m}})}$$ as $$\frac{V}{h^3}\int \log{...
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Sackur-Tetrode eqation becomes negative

The Sackur-Tetrode equation, tells us the entropy of of an ideal microcanonical gas. It looks like this: $S(E,V,N) = kN\text{ln}(\frac{V}{N}(\frac{E}{N})^{3/2})+ kN\cdot c(m)$ Now let's fix the mean ...
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Mixing entropy for ideal gases is decreasing

Consider two ideal (microcanonical) gases with particle number $N_{1/2}$, energy $E_{1/2}$ in a box with volume $V$. Also let's assume $\frac{E_1}{N_1} = \frac{E_2}{N_2}$. Let's call the corresponding ...
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Why is $\delta U$ not zero in $\delta H = \delta U + \delta(PV)$ while defining at a constant temperature for an ideal gas?

I was studying thermodynamics and came across the relation between change in internal energy and the change in enthalpy for an IDEAL gas, meaning $U=f(T)$ and not $f(T,V)$. Then, while defining it for ...
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Can a fixed amount of ideal gas undergo a reversible process when 2 of either pressure, volume, or temperature are held constant?

I've seen some problems where this was the case: a fixed amount of ideal gas underwent a reversible process where temperature varied while pressure and volume were both held constant. How could that ...
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How would I calculate the heat change of compressed air?

My friend is working on a snow gun, which involves using compressed air to blow apart water coming out of a pressure washer. I read that you can cool air by compressing it, which makes it hot, then ...
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