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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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What is the meaning of $PV^\gamma=$ constant in an adiabatic process?

In an adiabatic process, heat transfer doesn't occur and hence $\Delta U=-W$ (an increase in internal energy due to work done on the system or a decrease in internal energy due to work done on the ...
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Difficulty in calculating effusion rate using the kinetic theory of gases and statistical mechanics

I have tried multiple sources and methods, but my attempts at a proof of the number of particles leaving a gas using statistical mechanics keep finding the same wrong result. I have tried to read ...
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Confusion while deriving kinetic-molecular theory of gases

How many of the molecules will collide within a given area A of the wall normal to the x-direction in some fixed time interval Δt ? On average half the molecules have a positive x-...
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Can some one explain following formula for average impulse of a molecule in the derivation of Boltzmann–Gibbs distribution

Thus, the total average impulse contributed by a molecule with an $x$-component velocity ranging between $v_x$ and $v_x+\mathrm dv_x$, is given by $$2mv_x\cdot\frac{v_x\tau}{L_x}\cdot\sqrt{\frac{\...
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Atmospheric pressure, density and temperature variation with altitude

I'm trying to understand how one can calculate pressure, density and temperature of the atmosphere as a function of altitude. My assumptions are mostly sourced from https://en.wikipedia.org/wiki/...
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Ideal gas law in combustion engine analysis

I'm studying this derivation of the Diesel engine theoretical efficiency: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/diesel.html Here the ideal gas law is used in many occasions. Why is it ...
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Why is potential energy zero in this calculation of partition function?

In section 7.2 of Rief's "Fundamentals of Statistical and Thermal physics". While calculating the partition function for ideal gas he writes: $$ \begin{array}{l} \displaystyle{Z' = \int{ \...
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Difference between ideal gas and perfect gas?

I tried seaching it in the internet but I didn't understand anything. I know the definition of ideal gas. But I don't understand what perfect gas is. Can you help me, please?
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As I inflate a balloon at a constant temperature does the pressure of gases inside it on the balloon increase?

I know it's a dumb question but I am having a little misunderstanding with Boyle's Law. Shouldn't pressure be inversely proportional with Volume , or this is meant for the pressure outside of gases ...
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Temperature increase of a gas in a period of time [closed]

Pardon my simple question for you physics geniuses but: I'm attempting to simulate hot air balloons for a game. I have a gas of known volume, temperature, pressure and density inside a confined space....
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Is translational/rotational KE conserved when diatomic molecules collide?

When two diatomic molecules of a gas collide, is the collision elastic or inelastic? Is rotational KE also conserved/not conserved? My guess is that translational KE is conserved while rotational KE ...
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If we push a syringe with gas in it In space , would its temperature increase permanently , Violating Boyles Law?

On Earth If we push a gas syringe very fast Inwards , work is done on the gas by W = PV which increases the Kinetic energy of molecules in it and since Temperature is Average Kinetic Energy ...
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Does Temperature decrease on increasing No of mol of a gas in container ?

ideal gas Law says that PV/T = nR So does lets say you increase n and you Keep P and V constant should'nt the temperature decrease?
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Confusion between molar gas constant and boltzmann constant?

So after reading reading through internet I came to the conclusion that : For gas of any element PV/T = Constant of proportionality and that constant of proportionality can be expressed in ...
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How much pressure is needed to create a can of compressed air duster?

First, I asked this question because I want to take advantage of a can of air duster cooling ability So if I want to make a can of air duster, how much pressure do I need? Can I use regular air ...
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63 views

In ideal gas $\partial_V(PdV)_T=P$

First $\partial_V(PdV)_T=\partial_V(PV)_T=P$ However, if write it by chain rule and $P=nRT/V$ $\partial_V(PdV)_T=P\partial_V(dV)_T+\partial_V(P)_TdV=P\cdot 1+\partial_V(P)_TdV=P+P=2P$. What's wrong ...
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Is RMS velocity of gas particles always larger than the average velocity?

Is the root-mean-square velocity of gas particles always faster than the average velocity? I've done a couple of calculations with both and that seems to be the case; however can you make a formal ...
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Computing entropy for two ideal gas systems

I'm trying to show the processes in the following rows are different. So on the left there are $12$ particles in each box with volume $V=V_1$. Both are divided in three imaginary and equal parts with ...
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Ideal Gas Expansion

I'm confused how to understand this problem - One mole of an ideal gas at 300 K in thermal contact with surrounding expands isothermally from 1 lit. to 2 lit. against a constant pressure of 3 atm. In ...
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721 views

Earth-like Atmosphere Breaks Second Law of Thermodynamics due to Conduction?

Consider a neutral gas around an Earth-like atmosphere with density, pressure and temperature given by $\rho,\ p$ and $T$ respectively. To keep the system a closed system assume that the atmosphere is ...
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Piston cylinder assembly with separate compartments [closed]

Consider an ideal gas in a piston cylinder assembly, initially divided into 3 compartments by impermeable diathermal membranes. The compartments initially have the same mass and temperatures, but ...
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Ideal gas law for a gas with nonuniform temperature

Consider a piston-cylinder assembly with an axial temperature distribution $T(x)$ in the gas. The entire system, however, has a uniform pressure. Can I still apply the ideal gas law $PV = nRT(x)$?
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Isn't the equation of state for ideal gas valid in the free expansion?

I am deeply confused.... For a thermally insulated ideal gas expanding freely, I think that $PV^{\gamma}=cnst$ must hold. Through the equation $PV=nRT$, it must be that $TV^{{\gamma}-1}=\rm constant$. ...
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Forces on piston

When we heat any container containing a gas fitted with a piston, a part of the heat energy increases its internal energy and the rest does work on the piston. But when the gas does work the piston, ...
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Effect of mass on gas pressure

I know that PV=nRT and this equation does not take mass into consideration. However P is also =Force/Area. And weight is a force which is equal to mg. Will gas pressure be dependent on the mass of ...
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Isothermal bulk modulus of an ideal gas

To calculate isothermal bulk modulus, I have two methods. Method 1: $P_1V_1=P_2V_2=K$ $B=-\dfrac{(P_2-P_1)V_1}{V_2-V_1}$ $B=-\dfrac{(\dfrac{K}{V_2}-\dfrac{K}{V_1})V_1}{V_2-V_1}$ $B=-\dfrac{\dfrac{...
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Why does frequency of collision increase as volume decreases?

Today I was presented with the following scenario: A syringe with one end sealed and with a frictionless piston is dipped into cold water. What is the change in frequency of collision(ie, more or ...
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Ideal gas assumption for the Temperature Jump Distance calculation

I want to calculate the contact conductance between two surfaces that have a thin layer of air (on the order of micrometers) between them. A quick literature review shows that the heat transfer ...
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Why does $H_2$ have $C_V$=$7/2 R$ at high temperatures, while the total number of degrees of freedom is 6?

The two hydrogen atoms have 6 degrees of freedom in total. Of them, $3$ contribute to translation, $2 $contribute to rotation and $1$ contribute to the vibration. I know that the vibrations motion is ...
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How do I calculate the height of a given that a bubble rises from the bottom of the lake to the top of the lake? [closed]

I am stuck on a physics problem which involves calculating the depth of a lake given that a bubble increases two times in volume as it rises from the bottom of a lake to the top of the lake. The ...
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How to calculate increase in pressyre from LN2 phase change

I am trying to calculate the increase in pressure caused by liquid nitrogen when it changes from liquid to vapor within a closed, constant volume at atmospheric pressure. The liquid nitrogen fills 100%...
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Ideal gas in piston with resistor, isothermal expansion, calculate velocity

I have this problem from Resnick's Physics, 5th ed, problem 31-15, sorry I only have the Spanish version (i'll translate): A resistor R=550 ohm, connected to an external battery, is inside an ...
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Any physical basis for this pressure vs flow model across flow restriction?

Recently read a journal paper on biomedical engineering where the authors used the following expression to model the expected volumetric gas flow, $Q$ from a pressure potential $\Delta P$ : $$\Delta ...
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Negative Heat Capacity of an Ideal Gas

Sign Conventions:- Work if done by system, heat given to system and Increase in Internal Energy implies $+$ change. Otherwise $-$. Ok, consider an ideal gas in a container with perfectly conducting ...
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diffusion of gases in both directions

I am a technical specialist that works on analytical equipment. Gas chromatographs use carrier gases like helium and hydrogen that flow through long, thin glass tubes coated on the inner surface with ...
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112 views

Canonical ensemble near absolute zero

In the canonical ensemble for an ideal gas of $N$ bosons, the partition function for $T\to 0$ scales like $$Z\sim e^{-\beta\epsilon_0N},$$ when $\epsilon_0$ is the lowest (non-degenerate) single ...
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Sound pressure levels: Why doesn't blowing in someone's ear cause hearing damage?

Quoth Wolfram Alpha: 5000 Pascals ≈ 0.51 × lung air pressure that a typical adult human can exert (≈ 9800 Pa) ≈ 50 × sound pressure at the threshold of human pain (≈ 100 Pa) And yet the ...
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egg in the bottle demo gas law identity

so, i've taught chemistry and physics for 15 years, and yet i still need help with this. the classic egg in a bottle demo i'm referring to is the one done with a lit object being placed in the bottle....
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Is the ideal gas equation valid for a flowing fluid?

The assumptions for an ideal gas are: the gas consists of a large number of molecules, which are in random motion and obey Newton's laws of motion; the volume of the molecules is negligibly small ...
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Star formation from gas? [closed]

Considering the ideal gas law , where pressure is always positive, i wonder : How can gravity turn a gas into a star? Yes gas has mass too. But a light gas obeing the ideal gas law seems ...
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Do ideal gasses really not interact with each other at all?

I'm having trouble understanding how two different ideal gasses occupying the same space affect/interact with eachother. Presumably, the answer to this question is as in the title: Ideal gasses do not ...
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Gas and liquid at different temperatures. How do I read the pressure?

I am a homebrewer. My setup holds 6 5-gallon kegs. Previously I had my CO2 inside the chest freezer I've converted into keezer. I've recently acquired a 6th keg and there is not room for both 6 kegs ...
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Work done by isothermal gas expansion followed by an isobaric expansion

A mono-atomic ideal gas of $2$ moles undergoes an isothermal expansion which makes its volume double. Then the volume of the gas is doubled again through an isobaric process. Given a starting ...
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Entropy of the ideal gas - How to derive the $S(U,V,N)?$

I'd like to derive the $S(U,V,N)$ function. In the lecture, we were using the $S=k_b \log(\Omega)$, some combinatorics, approximation, $6N$ dimensional spheres, etc. But I'd like to avoid that if it's ...
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Calculating entropy for the surroundings the logical way doesn't work

EDIT: I was missing the entropy change due to temperature change and now everything makes sense Suppose I have $n$ mol of an ideal gas in a chamber with a piston with volume $V$ at pressure $P_{1}$ ...
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Bulk viscosity in jump conditions for shock waves

One of the jump conditions for shock waves can be derived from the Navier-Stokes equation and it takes the form (see Shu, Gas dynamics, p.212) $\dfrac{d}{dx}\left(\rho u^2 + P - \frac{4}{3}\mu \frac{...
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Maximum velocity of piston pushed by a gas on adiabatic irreversible expansion [closed]

I am currently studying for my country's IPhO selection process and thermodynamics has to be one of my favorites right now. However I came across a very odd problem that is making me revise a lot of ...
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What is the difference between $\langle v^2 \rangle$ and $\langle |v|\rangle^2$?

Let us take an example: the ideal gas. I know for example that $\langle v \rangle^2$ is different than $\langle v^2 \rangle$, as $\langle v \rangle=0$ due to no preferred direction. But know if I ...
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Using the work-energy theorem in thermodynamics

If an $n$ moles of an ideal gas (one atomic) is heated at constant volume $V$ from temperature $T_1$ to temperature $T_2$, the amount of energy heat needed can be calculated as $$ Q = nC_V \Delta T $$...
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Is Avogadro's law applicable for atoms or just for molecules?

I notice that online definitions of this experimental law always say, molecules or atoms. From the Wikipedia article on Avogadro's Law: $${\frac {V_{1}}{n_{1}}}={\frac {V_{2}}{n_{2}}}$$ The ...