# Tagged Questions

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

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### How do I compute mass flow rate for a compressible fluid?

Consider the vacuum chamber in the figure. If a hole with cross section area $A_{cs}$ is created, how can I approximate the maximum mass flow rate, $\dot{m}$, for a compressible fluid (e.g. air)?
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### Is it possible to consider PV diagrams without the equations of state?

Suppose that we have the equations of state for a particular system, or equivalently, that we have the fundamental relation $S = S(U,V,N)$. If we want to write down a PV diagram it will be quite ...
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### The average value of the electric polarization of an ideal gas

An ideal gas consisting of $N$ molecules possessing an electric dipole moment $\mathbf{d}$, placed in a constant electric field intensity $\mathbf{E}$. Need to calculate the average of magnitude of ...
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### What is meant by a “change in volume of a system”?

I keep getting confused when my professor talks about the change in volume of a system. Sometimes it seems as though he's talking about the volume of the gas and at other times he might be talking ...
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### Free expansion of ideal gas, transient phase (3 questions)

We all know the classic scenario of free expansion. A contained gas expands into a vaccum and in the end we have $\Delta T = \Delta U = \Delta H = 0$ and $\Delta S = R \ln \frac{V_2}{V_1}$. This is ...
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### How Heat is constant in adiabatic process

Consider adiabatic cylinder with a piston attached. $Q=0$ in this case and Work done is equal to change in internal energy. If I do work on the piston then its internal energy increases and so its ...
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### Chemical Potential in the canonical and grand canonical ensemble

I'm studying the ideal Fermi gas from "Statistical Mechanics", by R. K. Pathria. In particular, the following formula, which can be found on page 237: \mu=\left(\frac{3N}{4 \pi g V}\...
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### Would a hybrid mixed medium balloon allow you to use less helium to lift equivalent weight?

Suppose you had two balloons, one inside the other (a inside b). Would filling balloon "a" with the 80% nitrogen/20% oxygen mix you find in the surrounding air at ground level, and then filling ...
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### Why does the expansion of gas into a vacuum mean that we have less information about the system? (entropy)

I'm reading through Statistical Physics by F. Mandl and in the chapter about the 2nd law of thermodynamics he states that: The basic distinction between the initial and final states in such an ...
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### Calculating heat absorbed from expanding gas [closed]

I'm trying to calculate the amount of heat absorbed per kg of different types of gas, namely compressed air and carbon dioxide. Starting with carbon dioxide, I found that the Joule-Thompson ...
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### pipette waterfountain

Place the tip of a pipette in some hot water. Cover the other end with you thumb. Invert the pipette and water sprays out nearly two metres. Is the cool air in the pipette being heated by the hot ...
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### Compute $\langle x^2\rangle$ for gas of non-interacting particles in a quadratic potential

Consider a 3d gas of $N$ non-interacting identical particles in a quadratic potential, where the Hamiltonian $H$ is: $$H = \sum_{i=1}^N \bigg( \frac{p_i^2}{2m} + \frac{k}{2}x_i^2 \bigg).$$ After ...
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### Can't change in momentum be negative?

I was going through a derivation, of Ideal gas equation, PV=1/3 mnc2 and the book showed the following... But I know that change in momentum should be final momentum-initial momentum. But if it is so ...
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### Calculate the pressure in a container given moles and volume [closed]

Say there are two containers with the same volume. The first has a temperature T and pressure P and contains 1 mole of $O_2$. The second has a temperature 2T and contains 1 mole of $He_2$. I'd like to ...
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### Acceleration of an bubble under the sea [duplicate]

An air bubble arises from the bottom of the sea. Find its acceleration if resistance force is proportional to $\rho Av$ where $\rho$ is density of water, $A$ is cross section area and $v$ is velocity ...
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### Can the internal energy of an ideal gas system increase as temperature decreases?

If $\Delta U = Q + W$ Then adding $x$ moles of an ideal gas of lower temperature into a system of internal energy $U$ would increase $U$ as the kinetic energies of the molecules of the colder gas ...
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### Gases Expanding and Bonding in the Vacuum? Frozen Clouds

Why do gasses expand in space rather than attract forming a liquid? Do some gasses attract or bond when they get colder and what would be the characteristics of it in space? Would it be like powder ...
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### Kinetic theory of physics [closed]

$$E = (3/2) kT$$ For average kinetic energy of a molecule gas.The constant $k$ does not depend on the type of molecule. Can this result be true for both hydrogen and chlorine?
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### Understanding the relation between pressure, ideal gas and, volume

I was given the following formula which is used for ideal gasses: $$pV = nRT$$ where: p:pressure V: volume n: number of moles R: gasconstant T: temperature now when speaking about vaporpressure ...
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### When does $PV = const$ stop being true?

My problem is the following: a 15-liters cylinder contains air compressed at 370 bar. How many liter will flow out of the cylinder once uncompressed at 1 bar? I thought that I could use $PV = const$ (...
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consider a mole of an ideal gas enclosed in a container with a mass-less piston undergoing isothermal reversible expansion. now we know that in an reversible process the system and the environment ...
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### Enthalpy of condensation

suppose we have one mole of an ideal gas undergoing a phase change at constant temperature. we know that enthalpy change is given by the formula $n\cdot Cp\cdot\delta(T)$. since there is no ...
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### Calculate Liters Remaining in a CO2 gas cylinder/bottle [closed]

I know: The gas is CO2 (very close to 100% CO2) V - The Volume of the Cylinder (constant) P - The pressure of the Cylinder (from a sensor) T - The temperature of the Cylinder (from a sensor) I ...
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### The Balloon Model for Human Ventilation

The balloon model is often used to show how ventilation works in the human lungs. You pull on the diaphragm, expanding the volume of the container, and the balloon begins to fill up. My understanding (...
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### How long it takes till the gas reservoir is empty?

We have a gas reservoir of internal pressure $p$ filled with an ideal gas of volume $V$. The gas is leaking to outer atmosphere till the internal pressure equals atmospheric pressure $p_0$. The ...
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### if there is Ideal Gas constant, then do we have real gas constant?

We have Ideal gas constant for ideal gases. But ideal gas is very hard to make or to be found. So we have real gases in nature. Now there is 'real gas equation' (also called 'Van Der Waal's equation') ...
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### Filling of a gas in a cylinder

The problem statement is as follows: An insulated rigid vessel of volume $V$ initially contains $N_i$ moles of an ideal gas at temperature $T_i$. A pipe is now connected to the vessel and the same ...
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### Understanding why 2*density of a isolated gas equals half the initial temperature

A vertical cylinder of cross-sectional area 0.050 m2 is fitted with a tight-fitting, frictionless piston of mass 5.00 kg. The cylinder contains 3.00 mol of an ideal gas at 227°C. At what temperature ...
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### Statistical mechanics of ideal gas in a box with adsorption states on surface [closed]

Assume we have a cubic box of side length 1m with ideal gas particles inside. We assume the binding energy of a gas molecule to the wall is 1eV. One can make the simplifying assumption that: ...
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### Adiabatic expansion of ideal gas and dependence of temperature on volume

We know that for an ideal gas $$PV=nRT,$$ where $P$ is pressure, $V$ volume, $n$ amount of substance in moles, and $T$ the temperature of the gas. We can easily derive that, for a (non-free) ...
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### Thermal Energy in a pV diagram

I'm studying for an exam in thermodynamics and therefore going through old exams, but I am stuck on one assignment. One kilomole of ideal monoatomic gas under standard conditions is processed ...
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### How do you calculate oxygen temperature as atm pressure changes? [closed]

I know that when gases are decompressed the atoms suddenly have a bunch of space and absorb all the heat around them thereby giving the effect that it is cool but how do you calculate this for oxygen ...
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### Gasses and Gravity

I have two questions. First question. When gas is placed inside a container it fills the container evenly with constant pressure. If the container size varies the gas expands or is compressed but the ...
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### Oblique collisions in classical gas

I am trying to simulate the collisions in classical gas. So the particles are point like and have identical mass. It is easy to find who collides with whom but the what happens to the particles after ...
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### Gauge Pressure and Bar Pressure [closed]

I ran into a problem trying to calculate the absolute pressure of an isolated system. I was given that the gauge pressure in a tire is 200kPa or 2 bars. To get the absolute pressure I would have to ...
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### Ideal gas law with two types of gases

Suppose a container with volume $V$. If I put 2 different types of monoatomic ideal gas, say type $A$ and type $B$, such that there are $N_1$ particles of gas $A$ and $N_2$ particles of gas $B$, with ...
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### Liquid phase is a highly compressed gaseous phase

$\mathbf{Q:}$ While teaching "Real Gases", my professor remarked last day that "Liquid phase is a highly compressed gaseous phase." But he did not explain the reason behind it and left it as food for ...
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### Energy of classical ideal gas in the grand canonical ensemble

The canonical partition function for an ideal gas is $Z(N,V,\beta) = \frac{1}{N!} (\frac{V}{\lambda^3})^N$ where $\lambda = \sqrt{\frac{\beta h^2}{2 \pi m}}$ is the thermal De-Broglie wavelength. It ...
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### RMS Speed of Gas Molecule for Polyatomic Molecules

Halliday in his book and also many people say that RMS speed, $v_{rms}$ is $\sqrt{\frac{3RT}{M}}$. However, he used this formula in showing that kinetic energy, $K$, is $\frac32kT$. but how about ...
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### How does a gas emit radiation with temperature when it's particles motion are linear?

Particles in gas move faster with temperature in a linear motion (root mean velocity equation?) right? It explains increase in pressure and effusion proportional to temperature. Solids emit radiation ...
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### hot air balloon and pv=nrt [duplicate]

[on hold] up vote-3down votefavorite A hot air balloon has a total mass 750 kg (not including the air in the balloon) and holds a volume of 2.8x10^6 L of air. Assume the density of air outside the ...
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### Why is it not possible to use the ideal gas law to determine if the pressure changed in this situation?

I was given this question for my homework: A cylinder with a valve at the bottom is filled with an ideal gas. The vale is now opened and some of the gas escapes slowly. The valve is then closed, ...
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### Thermal conductivity of a binary gas mixture

I want to estimate the thermal conductivity of binary gas mixture, say water vapor+nitrogen. I assume the mixture as ideal gas. The molar fraction and thermal conductivities of the components are ...
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### What is a good software for Ideal Gas simulation?

I am looking for a software that simulates the microscopic behavior of an ideal gas, something like this: http://www.youtube.com/watch?v=tEFHkcx2cz0 (unfortunately this program is not openly available)...
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### What is the cause of this 'bump' in the heat capacity graph for a monatomic ideal gas?

I am trying to understand the heat capacity behaviour for an ideal gas as a function of temperature. The text I am learning from is Schroeder's An Introduction to Thermal Physics. This is an exercise ...
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### If Gravity acts on the particles in the gas, why don't they accumulate on the lower surface and fall down?

A quantity of gas is enclosed in a metal cylinder fitted with a piston. There are very many gas molecules.The cylinder walls are thermally conducting. Now, the question...
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### Thermodynamics: Deriving inner energy from ideal gas equation of state [closed]

If we know equation of state for ideal gas $PV = NkT$ where $P$ stands for pressure, $V$ for volume, $N$ for number of particles, $k$ is Boltzmann constant and $T$ is temperature, how can one ...
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### Time between two collisions in a 2D gas

I'm trying to code a simulation of a 2D gas in a box. The molecules are represented by circles of radius $R$ having elastic collisions with the walls only (for now). I read that the average time step ...