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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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Is Internal energy a function of pressure?

I read that internal energy is a function of temperature only and not pressure. But say, we compress a volume of gas. Won't the particles start moving more quickly? Meaning an increase in their ...
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II law of thermodynamics & polytropic process

The polytropic process is defined as such that $pV^m=A$, where $A$ is a constant. Generally, the change in entropy is $$\Delta S=nR \ln \frac{V}{V_0}+nC_V\ln \frac{T}{T_0}.$$ Using $pV=nRT$ and $pV^m=...
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Gas Transport Problem

I have a question that I thought would be a very simple effusion calculation that sent me down a massive rabbit hole after I tried to look it up in Landau's Physical Kinetics and so now I'm coming to ...
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The force exerted by a single molecule

In the chapter of the kinetic theory of gases in a basics undergraduate physics book, it says the force exerted by a single molecule on a wall is calculated as $F = \frac{\Delta p}{\Delta t} = \frac{...
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1answer
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What would be the distances between compressors part of a gas pipeline from Earth to the Moon?

This paper, acquired from this question about tethers on the Moon, describes LADDER, a mission to deploy a Lunar Space Elevator [LSE]. The space tether, made of Zylon fiber, would be 264,000 km long, ...
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Is it possible for temperature to cause a change in the density of air in a closed isochoric system?

I am taking a meteorology chair as part of a airline transport pilot course and while discussing atmospheric pressure and density the professor claimed that an increase in the temperature of the air ...
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21 views

How to get equations of state by differentiating a thermodynamic potential?

For an ideal gas in a closed system, the thermodynamic potential U, the internal energy, is given by $$ U(V,S) = U_0 \left( \frac{V_0}{V} \right)^{2/3} \text{e}^{\frac{S-S_0}{C_V}},\quad C_V = \frac{...
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76 views

Does the entropy of a real gas increase or decrease as compared to the entropy of ideal gas when the gas compartment is expanded so $V_f > V_i$

so i know the derived equation for change in entropy of a real gas but im struggling to understand how to compare that to the change in entropy for an ideal gas to answer the above question
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Re: Charles' Law: Is there a real world or laboratory example of an increase in volume under constant pressure CAUSING an increase in temperature?

Re: Charles' Law: V/T = Constant, i.e., V and T are directly proportional; that is, assuming a constant pressure and amount of an 'ideal' gas. It is easy to understand that the volume of a gas ...
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107 views

Gibbs theorem and partial molar volume

In the above, it's mentioned that any quantity other than MOLAR VOLUME can be written that way. But how can we say generalize it with certainty when molar volume itself doesn't fit in or to say any ...
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Deriving simple equation for volume and pressure, adiabatic exponent

I have $$VT^\frac{f}{2}=\text{constant}\tag1$$ and $$V^{\gamma}P=\text{constant}.\tag2$$ Where $V=\text{volume}, \ P=\text{pressure} , \ T=\text{temperature},$ $f=\text{number ...
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Potential energy of an ideal gas

According to equipartition theorem, for ideal gas in thermal equilibrium, each vibrational mode will get $kT/2$ for kinetic energy and $kT/2$ for potential energy. But at the same time, we assume ...
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33 views

Converting Gas volume to Liquid Volume

For a test setup, I need to set CO2 flowrate as 130 L/h but I do not have a flow measuring device to set it. So I made one device as mentioned below. Once I set the flowrate, I will remove containers/...
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Internal energy of ideal gas in terms of sound speed and pressure

In thermodynamics two state variables can be treated as independent and any other variable can be determined from these two variables. We can assume sound speed and pressure as independent variables ...
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1answer
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Particle in kinetic gas theory without collision

Hello I have a (Gedankenexperiment) question about the kinetic gas theory. As far as I understand temperature corresponds to kinetic energy. Assume now there would be one particle that does not ...
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22 views

Is there a word for the availability of a gas, normalized for pressure?

As a bit of background of what I'm getting at, consider that for the purposes of humans breathing and getting oxygen into their blood, 20% oxygen at 1 atm is equivalent to 100% oxygen at .2 atm. ...
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1answer
51 views

Is internal energy frame-dependent? [duplicate]

In the realm of kinetic theory of gases, the internal energy of gas is solely due to the sum of kinetic energies of all particles, since kinetic energy is frame dependent I was thinking whether a ...
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43 views

(SOLVED) Calculate the velocity of a gas inputted in pressure difference

I'm trying to make a generally simple calculation but I'm not sure if I'm approaching this correctly. So as I'm making assumptions solving this problem, please comment or correct me wherever I'm wrong ...
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2answers
61 views

On internal energy conservation in a gas system

I have seen multiple questions which talk about a tank with a partition in the middle and different ideal gases on either side at some different value of pressure,volume and temperature and then they ...
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41 views

What happens when ideal gasses are mixed?

I'm sure their temperatures will be equal, but what about their volumes and pressures?How does one approach ideal gas mixing problems?
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What does $C_p-C_v=R$ mean? What are its applications?

So my question is: what does $C_p-C_v=R$ actually mean? It's very straightforward to derive. But my issue is, where and what use does this have in real life applications, and why is it important? All ...
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What happens to the pressure and the temperature of a gas compressed adiabatically?

The set-up is basic. There is a piston that goes down, reducing the volume. The process is adiabatic, so the acquired energy is kept inside the gas. The ideal gas law states that as the volume ...
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Is it possible to calculate pressure without a barometer?

For an experiment, I need to pump air into a rocket with varying volumes of water, and thus air. However, I want to keep the pressure the same. Given the amount of air a bicycle pump can pump, the ...
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1answer
67 views

Pressure in a 2D Ideal Gas simulation

I am currently creating a 2D ideal gas simulator whereby the user can determine three of the four variables (P, V, n, T) and the gas would adjust accordingly. I was wondering how I could calculate ...
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126 views

Expansion of an ideal gas in an evacuated bottle having nonconducting walls

In the free expansion of ideal gas in a vacuum $dW = 0$ as $p_{ext} = 0$ and $dU = 0$ therefore there is no change in temperature of the ideal gas also. what i want to know that can the following ...
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Finding the temperature of a gas using the $P$-$V$ diagram [closed]

I need to know a way to relate the P-V curve of an ideal gas to its temperature.I found a similar question on stackexchange but couldn't understand how the relationship between a point and the ...
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Reason for gas constant value

I know that it's derived from experimentation and it's natural but is there a specific reason that the value is $8.31\space J\space mol^{-1}\space K^{-1}\space$?
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Find the density of air at the given temperature and pressure [closed]

Find the density of air at $99$ kPa and $322.15$ K. My attempt: Let's assume that air is $78\%$ nitrogen and $22\%$ oxygen by volume. Average molar mass of air = $0.78\times 28+0.22\times 32\approx ...
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How do I calculate the pressure on the walls of my MD simulation?

So I've built a simulation in vpython where I have multiple hard balls that collide with each other and with the walls of the cube I've placed them in. I then replaced the values for their radius and ...
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Confused about summing over the velocity squared term

Consider a cubical box, L on each side. The box contains N molecules of ideal gas, each of mass m. All collisions are elastic. The force exerted by one molecule when it collides with a wall of ...
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Why maxwells speed distribution law doesn’t violet special theory if relativity [duplicate]

As per maxwells distribution law the molecule of gas will have speed across zero to infinity with some probability function. I want to know that why the speed above speed of light is possible (i know ...
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Ideal gas law when diatomic molecule is about to break into constituents

Suppose we have a diatomic molecule. Its center of mass has an average kinetic energy given by $$ \frac{1}{2} (m_1 +m_2) v_{cm}^2 = \frac{3}{2}k_BT $$ and using this we can derive the ideal gas law ...
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106 views

What is the volume occupied?

What is the volume occupied by 1 mole of gas at $10^{−10}$ torr, the pressure inside an “ultra high vacuum” (UHV) chamber. How do I solve this problem without being given the temperature?
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How do I simulate an ideal gas?

I wish to write a simple simulation of an ideal gas, but my maths and how I should have a model based the equation isn't quite up to it. I need some help understanding the relationship between ...
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Why is the probability that the collision angle will be in the range of 0 to 60 degrees than in the range of 60 to 180 degrees

Pretty much the title. It is given that the probability that the collision angle will be in the range of 0 to 60 degrees than in the range of 60 to 180 degrees I don't remember seeing such statement ...
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1answer
50 views

Work done by ideal gas under a reversible process which is not isobaric, isochoric, isothermal, adiabatic

First post, sorry for the poor formatting. Question Consider a non adiabatic system closed to mass exchange where an ideal gas traverses along a reversible path from state: to . What is the work ...
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102 views

Infinite entropy in ideal gas

Does it make sense that entropy goes to infinity as temperature goes to infinity? For an ideal monoatomic 1D gas I have an expression for entropy \begin{equation} S=Nk_{B}Ln(\frac{Ve^{\frac{5}{2}}\...
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Would setting the ideal gas constant to $1$ yield an attractive natural temperature scale? [closed]

In this recent question, there was a comment 'The "zero point" of Kelvin is natural, but the scale is not'. This led me to wonder whether setting $R = 1$ in the ideal gas law would be an attractive ...
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6answers
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Conversion of $R = 8317\ \mathrm{\frac{J}{kg\cdot mol\cdot K}} $ to $ 8317\ \mathrm{\frac{J}{kg\cdot mol\cdot {^\circ C}}}$

I'm trying to understand the unit conversions when one unit is obtained by shifting the value of another one by some constant. In particular, the unit conversions from Kelvin to Celsius scale: $$T(\...
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1answer
91 views

Why doesn't the equipartition theorem force the rotational energy of a monoatomic molecule to be significant?

I'm reviewing the Feynman Lectures and in them he states that the rotational kinetic energy of a monoatomic molecule in a gas is insignificant due to a small moment of inertia. But wouldn't the ...
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Transfer of gas particles during pressure change

There is a room with a known volume. The temperature and pressure are known too (STP). It is given that the window is open and there will be a pressure drop outside due to wind. I need to find the ...
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Collision frequency of ideal gas and velocities of molecule

Is collision frequency of gas molecule $ = \frac{V_{RMS}}{\lambda}$ where $\lambda$ is mean free path. Shouldn't it be $\frac{V_{average}}{\lambda}$? (I often see that in theories books suggest that ...
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80 views

Thermodynamics problems with a cycle (insufficient data?)

I am having some troubles in solving the following problem a professor gave us, and in my opinion I think that either there are insufficient data or the solutions are infinite. We have a perfect gas,...
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Question about a hand-waving estimation done by Landau

I was reading the book written by Landau on statistical mechanics (Statistical Physics I 3rd Ed). In §1 there is a footnote that Landau wants to illustrate how accurate a statistical average can be ...
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Does the ideal gas law apply to a moving vehicle?

If for example you have a car travelling along a road. There is obviously a high pressure region in front of the car, where the air is forced around the vehicle. Likewise, I understand that cars will ...
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22 views

How to calculate the actual pressure in chamber with reduced pressure but at increased temperature?

I would like to find out the actual pressure in a chamber (constant volume) where the pressure within is reduced to 1.5 kPa but with increased temperature to 65˚C. How to calculate this? Assuming 0....
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1answer
75 views

Kinetic Molecular theory ideal gases, deriving the equation $PV = \frac{1}{3}mN C^2$

The problem I have with this proof is how to acquire the fraction $\frac{1}{3}$. In theory we were taught by taking into consideration a rectangular vessel which obviously has three paths which a ...
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1answer
81 views

Momentum average on phase space for free particle

I'm studying from Greiner statistical mechanics, and he uses an approximation which I don't really understand. On averaging over many phase-space points we have $$\langle\vec{p}^2\rangle=3\langle ...
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84 views

Entropy density (entropy per particle)

How I can get this definition for an ideal gas: $s=C v \ln (Pρ^{−\gamma})+ \text{constant} $ ? In this answer it is mentioned that there is a connection with the Sackur-Tetrode relation of the ...
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Ideal gas equation vs Kinetic theory equation

From the ideal gas equation: $PV = NkT$, since Pressure times Volume = Energy, my understanding is that the total (internal) energy of $N$ molecules of a gas $= NkT$. However from the kinetic theory ...