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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3answers
518 views

Does Humid Air Rise (neglecting the effects of weather turbulence-for example in a closed environment like a sealed room)

An internet search will find many people claiming that Humid Air (water vapor) rises. However, I am skeptical because if lighter molecules rose then, it follows that the air would be stratified by ...
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1answer
362 views

How to find the work done by compressing gas?

What is the work done by the piston when the piston is compressed and there's no internal energy/heat lost from the gas(thermally insulated)? The reason I can't solve this problem is because I have ...
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1answer
513 views

External or internal pressure in the gas laws

Does pressure in the ideal gas law and other gas laws (Boyle’s, Charles’s, and Gay-Lussac’s) mean the external or internal pressure?
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673 views

Plotting a $PV$ diagram for free expansion — why is it undefined?

Apparently trying to plot a $PV$ diagram for an adiabatic free expansion of ideal gas is undefined. I'm taking issue as to why this is the case. From what I understand using my diagram attached as my ...
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How was the ideal gas equation derived?

How did people come up with the formula: $$PV = nRT = k_BT \qquad$$? I see two possible ways: 1.) We did some measurements and defined $$kB:=\frac{PV}{T},$$ remarking that $\frac{PV}{T}$ is ...
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103 views

Kinetic theory for Charles' Law: does frequency and time interval of collisions change?

So I was given this table in class about Charles' Law: The table I got from class says that the time interval and frequency of collisions increases. However, if the velocity of molecules and volume ...
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2answers
119 views

Ideal gas with sticky wall

A collection of $N$ point particles is held inside a cubic box of side $L$. The walls of the box are sticky. This means that when a particle collides with a wall, it stays attached for a short period ...
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1answer
137 views

Velocity for a straight line collision

I get that the force of a collision is m(Δv/Δt). What I do not get is why the change in velocity for a straight-line collision m(2v/Δt). Why is this?
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Does the internal energy of single-phase materials depend primarily on temperature or does it depend on pressure as well?

I am confused about the relation between the internal energy and temperature of ideal gases and single-phase materials. The following two statements from two distinct sources are mainly the reasons: ...
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1answer
2k views

Derivation of the virial expansion

It is easy to derive the ideal gas law form the kinetic theory of gases, but how do you derive the other coefficients of the virial expansion? Is it even possible to get a closed-form formula for the ...
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Why does the specific heat of a real gas depends on temperature but not for the ideal gas?

The specific heat of a real gas, unlike an ideal gas, depends on temperature. How can we physically understand this? Thanks.
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1answer
123 views

Different ways to perform an adiabatic expansion

In this Wikipedia article https://en.wikipedia.org/wiki/Joule_expansion#Entropy_production, three ways to perform an adiabatic expansion are mentioned. Irreversible non-quasistatic Irreversible ...
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63 views

Model to predict temperature of the Sun?

In a homework problem, we were to assume the Sun is a sphere with uniform density and use the hydrostatic equilibrium equation to compute the pressure at the center of the Sun? Upon doing this, I was ...
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1answer
651 views

A question on the ideal gas law and the functioning of a fridge

First let me apologize: I am not a physicist and my question is perhaps not well-suited for this expert forum. I didn't find any other place to ask though. We have the (simplified) formula $$ \frac{P ...
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63 views

Do gases mix faster when of unequal temperature?

Or, Is my room aired quicker during winter? I always feel that in winter, after opening the window, my study room becomes breathable quicker than in summer. Now, this is of course highly ...
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129 views

Internal energy

Internal energy at a specific state can't be calculated, but using kinetic theory of gases and the law of equipartition of energy, average kinetic energy is directly proportional to temperature. For ...
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1answer
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On HVAC Gauges, Why Are Pressure And Temperature Independent of Quantity?

I was looking at reading HVAC gauges and I noticed there are rings on the inside that indicate the temperature of the inside gas. These translate directly to the pressure of the gas. So if your gas ...
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791 views

Final temperature of mixing two different mass flows of the same gas in a different temperature and pressure

I've forgotten most of the terms involved in thermodynamics, so pardon me for using layman terms. I have a gas turbine and a wastegate that bypasses the turbine. The vessel in which the gas flows is ...
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What is an Ideal Gas?

I have read that there are no molecular interactions between the molecules of a gas, neither attractive forces nor repulsive. But how does that makes it an Ideal Gas. What are the effects of these ...
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188 views

Two gases seperated by semi-permeable membrane

The problem is as follows: Two ideal gases are contained adiabatically and separated by an insulating, fixed piston that blocks the molecules of gas 2 but allows the molecules of gas 1 through(in both ...
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112 views

Semi-permeable gas membrane [closed]

The problem is as follows: Two ideal gases are contained adiabatically and separated by an insulating, fixed membrane that blocks the molecules of gas 2 but allows the molecules of gas 1 through(in ...
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2answers
112 views

Why can't I use $U=\frac32 pV$ to find overall change in internal energy of the gas? [closed]

The physics question goes like this: An ideal gas undergoes an expansion in volume from $1.3\times 10^{-4}\:\rm m^3$ to $3.6\times10^{-4}\:\rm m^3$ at a constant pressure of $1.3\times10^5\:\rm Pa$...
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Are there equations that can describe the stretching of deformable container containing an ideal gas?

I have been studying the abdominal cavity and trying to draw analogies between what I learned in chemistry with ideal gasses and the abdominal cavity. However, the abdominal muscles and fascia are not ...
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1answer
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Temperature rise when filling gas tank from higher pressure tank

This is a more practical problem than theoretical, so hopefully that's acceptable on this site. I'm trying to fill a small tank with a gas from a larger tank at much higher pressure. The two tanks ...
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2answers
145 views

Can a mechanical fan increase ideal gas temperature?

Suppose we have a thermally isolated container of a homogeneous gas at temperature $T$. If, for example, the container is filled with xenon at STP, then we know that the RMS speed of each xenon ...
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Why does pressure remain constant during a phase change

Consider the following graph describing a phase change from a liquid state (blue area) to a gaseous state (light blue area). Why does the pressure remain constant in the coexistence area (grey area)?...
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How to model the ascent and descent of a high altitude (stratospheric) balloon?

I'm trying to create a MATLAB script that will plot the ascent, float, and descent of a high altitude balloon over time. The balloon should ascend to a pre-determined altitude, float around for a few ...
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1answer
101 views

On the average gas pressure over a pipeline

This question stems from gas flow through pipelines, quoting this paper (link): For the calculation of the $z$ factor one needs the average pressure $p_{av}$. An obvious choice is the arithmetic ...
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1answer
928 views

How do noble gases behave differently than ideal gases?

I've read that the behaviour of ideal gases is approximated really well by that of the noble Gases at high temperatures and low pressures. Suppose we manage to put some atoms of a noble gas into a ...
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1answer
316 views

Is atmospheric pressure exerts force from all directions of the object on the surface of the earth?

This question came to me as I was solving problem asks the length of the fluid in a open tube when the tube makes particular angle with horizontal surface by giving the height of the fluid when tube ...
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1answer
353 views

Is pressure Lorentz-invariant?

Consider a system of stationary 3-D ideal gas in the rest-frame $S$. This system is described by $PV=Nk_BT.$ Also, from the principle of equipartition, $E=\frac{3}{2}Nk_BT.$ Now we introduce a boost (...
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Inflating a bike tire with CO2, why does it go flat by the next day?

Typically when I get a flat I use a CO2 cartridge on the road. The tire is always flat and needs to be pumped up with air the next day. What is the difference in molecule size between CO2 and air (...
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1answer
197 views

Why does molecular potential energy increase with constant temperature?

You heat up a liquid at its boiling point, and the temperature remains constant until all the liquid has turned into vapour. Since the temperature stays constant kinetic energy stays constant too, but ...
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1answer
243 views

Probability depends on volume dependence of the multiplicity function?

The formula for the multiplicity of a monoatomic ideal gas is $$\qquad \Omega(U,V,N)=f(N)V^NU^{3N/2}$$ where $V$ is the volume of position space, $U$ is the molecule's kinetic energy, $N$ is the ...
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1answer
693 views

How can I demonstrate the internal energy of diatomic gas?

I want to demonstrate the formula to find the internal energy of an ideal gas. The formula is $$U = \frac{5}{2}nRT.$$ I first tried to use the formula $U = E_c + E_p$ (Internal energy of an ideal ...
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1answer
312 views

Avogadro's law and molecular sizes

As Avogadro's law states that equal volume of gases contain equal numbers of molecules at same temperature and pressure, then does it mean that all gases have same molecular size?
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541 views

Entropy of an ideal gas in $T\to 0$ limit

After deriving the entropy of an ideal gas we get to : $$S = Nk \left[\ln(V) + \frac{3}{2}\ln(T) + \frac{3}{2}\ln\left(\frac{2\pi mk}{h^2}\right) - \ln(N) + \frac{5}{2} \right]$$ In the zero ...
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Does the term “diatomic ideal gas” make any sense?

As per the kinetic theory of ideal gases, ideal gases are considered to behave as point particles that occupy negligible volume, and exert no intermolecular attractions. At the same time, diatomic ...
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1answer
162 views

Power of thermal radiation in gases

How much thermal radiation does a given volume of gas emit? Does it go according to Stefan-Boltzmann law, i.e. as $P=A\varepsilon \sigma T^4$, with $A$ as the cross-sectional area, $\varepsilon$ as ...
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3answers
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What is the pressure inside a closed bottle of air?

Is it equal to atmospheric pressure? If so why? Surely the amount of air particles inside the bottle is much lower than the amount of the air particles above the bottle (i.e. the column of air above ...
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1answer
2k views

How does the isothermal expansion of a gas increase entropy of surroundings?

I was under the impression that if a gas expands isothermally then energy must be transferred from the surroundings to the gas as it is performing work. But in that case surely using $$\Delta S= \frac{...
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1answer
444 views

Confused about ideal gas law with two types of gases

Suppose I have a ideal gas mixture consisting of two different types of ideal gases, say $A$ and $B$, in a container with volume $V_{tot}$. There are $N_A$ particles of gas $A$ and $N_B$ particles of ...
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1answer
2k views

Collisions of gas molecules with walls of a container [closed]

I am to calculate the rate of collision of gas molecules with the walls of a container with dimensions $3m\times4m\times2m$ at room temperature (20°C) and pressure 1atm. For reasons of simplicity I ...
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1answer
398 views

When do ideal gases stop behaving like ideal gases?

Sometimes I don't know which method I should use to calculate the volume of the gas in a system, I'm not sure if I should use the table values for the specific volume, or if I should calculate by ...
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2answers
9k views

Why is $PV^\gamma$ constant in an adiabatic process?

In non isolated systems where there is no adiabatic process, $PV$ is constant. But the graph gets steeper in adiabatic process because of the $\gamma$ over the $V$. Why is it there in adiabatic ...
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425 views

What does happen if I push a piston in an adiabatic cylinder containing an ideal gas?

What does happen if I push a piston in an adiabatic cylinder containing an ideal gas? According to Ideal Gas Equation: $$PV=nRT$$ Is it possible to predict what's going to happen? Will Temperature ...
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Sod shock tube - Contact Discontinuity

sorry for bothering with my question. https://en.wikipedia.org/wiki/Sod_shock_tube I have trying to understand, how is it possible to have a discontinuity on Density and not on Pressure. I don't ...
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1answer
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Nebulas and Ideal Gas Equation confusion

I was wondering how stars form and watched this video: https://youtu.be/mkktE_fs4NA?t=18s The lady says: "Gravity brings matter together. And when you bring matter together, when you squeeze ...
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If pressure is proportional to temperature, why aren't compressed gases always hot?

When you compress a gas, say within a deodorant can, it temporarily heats up, but then cools to room temperature whilst in the can. It will then cool down to below room temperature once decompressed. ...
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Ideal Gas and Thermodynamics

The question is : Let M and N be specific heat at constant pressure and specific heat at constant volume. M - N = a for hydrogen gas M - N = b for nitrogen gas Then find the relation between a and ...