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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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 ...
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How to calculate density of states for different gas models?

There are a couple examples I'm trying to understand, all in a box/square of length $L$: For an ideal gas in 2-D with $\varepsilon=\frac{\hbar^2k^2}{2m}$:$$ D(\varepsilon)=\frac{L^2m}{2\pi\hbar}\,.$$ ...
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Internal energy of an ideal gas independent of any thermodynamic variable at constant temperature

https://physics.stackexchange.com/a/199976/170242 In this answer (in the link), it is mentioned that "the internal energy of an ideal gas is independent of volume when considered as a function of ...
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108 views

Am I getting the definitions of these thermodynamics quantities right?

I started thermodynamics mostly through independent study and basically built up my own definitions of terms that appeared to fit with what was going on. They seemed to work but my question is whether ...
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Expansion work of monatomic gas [closed]

Monatomic ideal gas takes up Q heat, while its volume increases but the pressure stays the same. How many %s of the heat is for expansion work? I think it is an isobar process but how should I ...
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What's the difference between dP<0 and dP>0?

Assume a situation shown in the image1 below. The column is filled with gas. The number density is denoted as $n$, and the mass of each particle is $m$. Take the axis downward. By considering the ...
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Definition of chemical potential of an ideal gas contradicts equation of state?

My geometric intuition breaks down horribly regarding advanced concepts in thermodynamics, such as the use of thermodynamic potentials. My question here is therefore about the latter concepts (in ...
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1st law of thermodynamics mcq question [closed]

Given the following question: could someone explain how A is correct and D is wrong? I'm a little confused. Since its a closed cycle shouldnt there be no energy lost?
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ideal gas adiabatic process

I know how it is derived and here is my concern: $dU=-dA=-d(pV)$ p is not a constant here, it depends on V. So my logic says, ...
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Is entropy zero at temperature zero for ideal gas?

we know that internal energy of the system is defined in terms of temperature as $(3/2)kT$. so if temperature is zero so internal energy is zero. and that means that particle will not have much ...
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On the existence of ideal gases

I am following Statistical Mechanics course at the university, and my professor came up with this statement: Ideal gas model is nothing but a fictitious ideal system that doesn't really exist in ...
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Why is there a constant in the ideal gas law?

Why do we have constants? Consider, for example, the ideal gas law, $$PV = nRT \, . \tag{ideal gas law}$$ Sometimes I believe that the constant is there in order to make the equation work (make the ...
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Feynman Lectures I 40: Is the homogeneity of the Maxwell-Boltzmann distribution a result of, or a pre-requisite for its derivation?

I refer to hand-waving a lot in this post. That is not to say that it was in appropriate. Feynman pretty much said at the outset that his treatment of thermal physics was going to be less than ...
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117 views

Does the saturated vapor pressure depend on the external pressure or just only temperature?

So far I understand that the saturated vapor pressure is the pressure exerted by a substance in liquid (or solid) vapor equilibrium, and that this pressure depends on the temperature of the system. ...
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Difference between ideal gas law and saturated vapor pressure

Little bit confused on what each of these concepts are. So far i understand that the ideal gas law tells us how much pressure an amount of gas exerts on the walls of a container. I also understand ...
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Why the force is equal to minus the variation of the momentum for a gas particle hitting the wall?

Why when one calculates the force exerted by a gas on the wall we say that the force is equal to (for a single particle ): F = - $\Delta p$ . But to me , it should be : $F = (p$f $- p$i ) $= -p$i - $...
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Ideal gas reversible cycle

So I got this cycle on a quiz. As of my understanding, in the transformation 1-2 there is also received heat and given heat ( sorry if that's not the english exprimation, not my first language). Now I ...
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231 views

Boltzmann constant times absolute temperature

I came across a research paper with the following paragraph in a research paper. Research Paper section I am trying to fetch fluctuations from Kirchhoff's matrix and that is why I am interested in ...
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Thermodynamic Problem: Heating of House with Open Windows

I recently ran into the following interesting problem I am now stuck on: $$S = \frac{n}{2}(\sigma+5R\ln\frac{U}{n} +2R \ln\frac{V}{n}) $$ The air inside a house with open windows is initially in ...
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Demonstrating the average dot-product of relative incident velocity with CM velocity of colliding pairs of ideal gas atoms is zero

In The Feynman Lectures on Physics Vol. I Ch. 39: The Kinetic Theory of Gases an argument is given in 39–4 Temperature and kinetic energy, showing that the average value of the dot-product of the ...
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Understanding Feynman's development of the ideal gas law: Vol I 39-2 of The Feynman Lectures on Physics

In The Feynman Lectures on Physics, Volume I 39-2 The pressure of a gas, the following is presented: If $v$ is the velocity of an atom, and $v_{x}$ is the $x$-component of $v$, then $mv_{x}$ is ...
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Air coming out of balloon

I have discovered recently that when we have a balloon in a room filled with air, with temperature $T_1$, and then this balloon gets a hole and air is let out, the temperature of the air that comes ...
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Adiabatic expansion of ideal gas

I am considering a system with initial pressure $P_{A}$ and volume $V_{A}$. The internal energy $U_{A}$ should be zero. Then I have the following law for an ideal mono atomic gas $P^{3}V^{5}=const$. ...
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Thermodynamics and gaseous state combination question

A water vapour filling the space under the piston of a cylinder is compressed (or expanded) so that it remain saturated all the time,being just on the verge of condensation. Find the molar heat ...
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Wave equation on Air- Solid interaction

Suppose that there is, due to an explosion $h$ meters above the ground, a wave in the air with high density, velocity and pressure, capable of inducing an elastic wave on the earth's surface. How does ...
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Why do aneroid barometers have error with temperature?

Altimeters use slightly evacuated (compared to atmospheric pressure at sea level) metal aneroid wafers. The wafers have a reference pressure outside the aircraft referred to as the "static port". ...
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Why is the internal energy of a real gas a function of pressure and temperature only?

While studying thermodynamics, I read that the internal energy of an ideal gas is a function of temperature only. On searching the internet, i found an article which stated that the internal energy of ...
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Isothermal compression without a heat reservoir

I have devised a method to isothermally compress a gas without the use of a heat reservoir. Consider a container of gas. To compress the gas normally, one would simply move one of the walls of the ...
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Degeneracy in Maxwell Boltzmann distribution

While deriving Maxwell-Boltzmann distribution function we consider particles having degeneracy. But in classical mechanics how the concept of degeneracy of particle comes within?
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Will the discrete emission of Green House Gases (GHG) increase the global temperature by an infinitesimal amount?

Suppose you take a trip with a gas-guzzling car on a Sunday. Will your action increase the global temperature by an infinitesimal amount?
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Why are compressed air tanks cold? [duplicate]

Why is a compressed air tank cold to the touch when it’s in a compressed state before use?
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Perfect gases and gravitational field

I have made this reasoning, thinking about it for a time but it's time to ask to you for comments / opinions and solider advices. Let's take a perfect gas: we know the temperature is related to the ...
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Would a plane get lighter if dry ice is inside and it sublimes during the flight?

During a series of comments here, it was suggested that taking dry ice into an airplane, the airplane gets lighter as the ice sublimes. This was supported by the idea that when the dry-ice sublimes ...
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Internal energy of an ideal gas?

From my past studies I have had the presumption that for an ideal gas the equation: $du=c_v dT$ ( where $du$ is the density of internal energy, $c_v$ is the specific heat capacity at constant ...
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Why in an ideal gas as the volume increases, both the pressure and the temperature drop?

I was reading Fundamentals of Physics(Halliday, 10th ed.), chapter 19, when I saw a statement "Figure 19-15a shows our usual insulated cylinder, now containing an ideal gas and resting on an ...
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Example of reversible isochoric process for an ideal gas

I’ve seen many books considering reversible isochoric processes performed by an ideal gas. But is that possible? Suppose I’ve a general isochoric process going from A to B, suppose I’m having a ...
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Speed of Bubble in Coke

I was trying to solve the following problem, but my results seem illogical when I graph my solution. Assuming we have a bubble at the end of a coke glass, I want to solve for the speed of the bubble ...
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Relating the maximum entropy with the pressure given in terms of volume

For a monoatomic ideal gas let the pressure of gas in a container be given as $p=p_0- \alpha V$ Where $p_0$ and $\alpha$ are constants and $V$ is the volume of gas. Then find the volume at which ...
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669 views

Ratio of specific heats of mixture of gases

Suppose I have $1$ mole of a monoatomic gas and $1$ mole of a diatomic gas. If I mix them, the ratio of their specific heats at constant pressure to that constant volume becomes:$$\gamma = \frac{3}{2}$...
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Is the thermal energy of the an ideal gas equal to the sum of the kinetic energies of the individual particles?

I have been wondering about it all day as I heard that particles of bodies at absolute zero have no kinetic energy. So, is it true that the total kinetic energy of an ideal gas is equal to its thermal ...
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How do we choose the path when deriving the ideal gas law?

So, my textbook details the derivation of ideal gas law in this way: $$m_0v -(-m_0v)=2m_0v \tag{1}$$ $$F=\frac{2m_0v} {\Delta t} \tag{2}$$ $$\Delta t = \frac {a} v \tag{3}$$ $$F=\frac{2m_0v^...
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Why is the work done by the system equal P external x (V final - V initial)?

Please See this video https://www.youtube.com/watch?v=j_6JxoL8qD4 Firstly, at 1:13 in the video, is the work done here by the system or on the system? Secondly, are V final(s) in both cases equal? ...
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$h^3$ term in probability density function of ideal gas

Other than that we need the $h^3$ to 1) make the units correct and to 2) account for the normalization of the probability distribution, what interpretation can we give to this $h^3$ term in \begin{...
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What value does $\Phi$ take in this formula for ideal gas entropy?

In Wikipedia's ideal gas article there is a derivation for the thermodynamic entropy that results in $$S = Nk\ln\left[\frac{V}{N} \left(\frac{U}{\hat{c}_V Nk}\right)^{\hat{c}_V} \frac{1}{\Phi}\right],$...
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Chemical potential for ideal fermi gas with single particle energies $\epsilon_k^{\pm}=\pm \hbar c |\mathbf k|$

I came across the following question in some example problems for my graduate statistical mechanics course final exam: Consider an ideal gas of fermions of density $n$ in three dimensions with the ...
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In a gravitational field, will the temperature of an ideal gas will be lower at higher altitude?

I know there are similar questions, but I have some arguments which seem to explain that temperature of an ideal gas in a gravitational field will be lower at higher altitudes. I am assuming that: 1....