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

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Can the Sun's core be treated as an ideal gas?

I know that a gas behaves more like an ideal gas at higher temperature, and that is very well achieved in the Sun's core. But also low pressure is needed for a gas to behave like an ideal gas, and the ...
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45 views

Why we need to suppose the chemical potential is zero here?

I've been working on some statistical mechanics problems and one of them asks to compute the pressure with chemical potential zero of a boson gas whose particles do not interact and whose energies are ...
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1answer
26 views

Can I interpret Avogadro's principle of gases from the state equation (ideal gas law)?

Considering the molar form of the ideal gas law I can solve for the ratio of some gas volume, $V$ divided by the number of gas particles, $n$ in mols $$\frac{V}{n}=\frac{RT}{P}$$ And $R$ is the ...
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90 views

Why is it difficult to mix helium and nitrogen gases?

I recently learned an interesting fact: That it's difficult to mix helium and nitrogen gases in a compressed gas cylinder. Gas suppliers that need to mix the two gases have to rotate the cylinders for ...
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32 views

Monatomic gas work

Recently I was trying to solve the following problem: monatomic gas expanded from 0.2 to 0.5 m^3 and pressure increased from 404 to 808 kPa. Find work done by gas, heat gained and change in internal ...
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20 views

How abruptly would you have to brake to form an almost complete vacuum in the back seat? [duplicate]

Suppose you brake with a car (or any other moving object). As the air inside will rush forward, won't there be a relative dearth of air molecules in the back? So, how strong does the acceleration have ...
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34 views

If I double the amount of oxygen molecules, do I double the paramagnetic force?

Oxygen is well known to be paramagnetic. If I take one molecule, $O_2$, and measure its paramagnetic force due to externally applied magnetic field, and then add another molecule near the first ...
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22 views

Isothermal Atmosphere

I was taught that for isothermal atmosphere: $\frac{dP}{dz}=-\rho g$ How come the equation is only true for isothermal atmosphere? I suppose $dP$ can be caused by changed in temperature as well?
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37 views

Is it possible to have a line rather than a point where the three states of a substance can exist?

Most of us are familiar with state diagrams that define which of the three states a substance will take given the pressure and temperature. And that some substances, such as water for example, exhibit ...
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12 views

What is the heated added and changes in internal energy? thermodynamics

A piston + cylinder initially contains 2 x 10-3 m3 of helium gas at the pressure of 1.01 x 105 Pa and with a temperature of 60'C. The gas is heated allowed to expand at a constant pressure until its ...
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61 views

Pressure, density, volume and mass in a room

Here's the question. A window in the room is open. The next day, the temperature of the room has increased, but the pressure of the air stayed the same. State and explain what has happened to ...
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1answer
32 views

Triangular Cyclic Process

i am currently studying for my physics exam and i am trying to wrap my head around cyclic processes. There is the cyclic process - ![1]: (http://imgur.com/7i0JF1S) "cyclic process" We know its an ...
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50 views

Helium balloon stays on the floor

So yesterday I came back home with a buoyant helium balloon (no comment, and before you ask, it's blue) and I left it in the house. Obviously, it rose to the ceiling. This morning I woke up to a ...
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1answer
46 views

How does the bulk modulus of air change with rising pressure?

I can't seem to find the answer to what should be a trivial question: I have a rigid air-tight container of fixed volume and I am pumping air inside. The pressure is increasing (very slowly) from ...
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22 views

Can I always assume that a vapour pressure over a liquid is ideal?

Can I assume that the vapour of a subject over its liquid is ideal-ish? I'm thinking that if the vapour pressure is low the subject in question wont interact with itself, but it doesn't necessarily ...
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1answer
33 views

Static pressure in ducts and its dependency on speed flow and density

I know that depending on the duct circuit (bends, complex geometries...etc), the static pressure will be defined. If we assume air is flowing in the circuit with varying speed and/or varying density. ...
3
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1answer
76 views

Finding $p(z), \rho(z)$ of an ideal classical gas in a box

We have a classical ideal gas of particles of mass $m$ at fixed chemical potential $\mu$ and fixed temperature $T$. We have a potential energy $U(z)=mgz$ and the gas is in a rectangular box of height ...
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30 views

Pressure and force of ideal gas in a leaking container?

Let's imagine you have a container that has a pressure of 10 Pascals inside and a vacuum outside. The container has a volume of a cubic meter and I'm not sure if the temperature matters but lets say ...
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1answer
24 views

How do i check how much a gas deviates from ideality?

I have temperature- and pressure data from equilibrum between liquid and gas for an unknown compound. I have approximated the gas to be ideal and now that i have identified the compound, cyclohexane, ...
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64 views

How to calculate radius of a sphere of Ideal gas?

The problem I am faced with is approximating the mass of the sun, and I thought that a fancy approach would be to approximate the sun as being made up entirely of hydrogen atoms, finding the resulting ...
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1answer
24 views

What causes the black shimmering bands on a sun-lit surface?

I can't figure it out. I thought it was the window causing it, but even without it it happened. It seems to be the motion of the air that causes it, but why shimmering black bands? Sometimes this ...
3
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4answers
238 views

Where does air pressure come from?

Where does air pressure come from? I thought it was from gravity or the speed of the gas resulting from its heat. However, analyzing my own hypotheses, I think that my 'heat conjecture' is probably ...
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1answer
59 views

Derive the Sackur-Tetrode equation

How do you derive the Sackur-Tetrode equation? I know that you must start off with the multiplicity of a mono-atomic ideal gas: ...
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2answers
307 views

Why energy at room temperature $= kT$ and not $(3/2)kT$ [duplicate]

I always see that a room temperature of $T=300\,\text{K}$ corresponds to an energy of $k_BT \approx \frac{1}{40}\,\text{eV}$. But shouldn't it be $\frac{3}{2}k_BT$ since the molecules in the air have ...
3
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1answer
50 views

Is there an Ideal Liquid Law? Or Solid Law?

There is an Ideal Gas Law, but why isn't there one for liquids or solids? Is it because they are much too hard to predict or that solids and liquids vary drastically in their reaction to temperature ...
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36 views

How is convection possible in fluids, in the absence of a contact surface for any buoyant force?

I don't understand why liquids and gases are acted upon by a buoyant force. In a solid immersed on some fluid medium, the pressure pressure difference caused by gravity exerts a force on the surface ...
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52 views

In the Ideal Gas Law, what does “fixed amount” of gas mean?

Does it mean mass? If so, wouldn't Pressure/Temperature basically represent its density?
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75 views

How is the work done by a system turned into internal energy according to the first law of thermodynamics?

I have several questions about the first law of thermodynamics: When we have a force over a piston of a recipient with an ideal gas inside and that piston moves, we have work associated with that. ...
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1answer
24 views

plasma and infinite acceleration

I am trying to set up a simulation of particles (they are not any particular kinds of particles, they are just points that repel each other). All the particles repel each other through the inverse ...
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1answer
60 views

Zero volume at zero Kelvin

Why does the volume of a gas become zero at 0 Kelvin? Can a Bose Einstein condensate be considered as matter? (I mean the volume becomes zero)
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1answer
59 views

To find average speed of gas molecule when the temperature is incresed

We are given moles of gas let say $n$. Temperature is increased from $T_1$ to $T_2$. Volume is held constant at $V_0$. We need to find the average speed of gas molecule when the temperature $T_2$ is ...
0
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1answer
34 views

Amount of unknown parameters in compressible Euler equations

I'm looking at this page for the compressible Euler equations. To me it seems, in the 1-dimensional case, there should be 3 unknowns: density, velocity, and pressure. This is because the energy $E$ ...
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30 views

Thermodynamics Work Done At constant pressure and charles law

If we fix a piston in the mouth of a cylindrical container in such a way that the piston settles when the pressure from outside the piston is equal to that of the gas within the container, and ...
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1answer
37 views

Viscosity for steam in the Reynolds number

In calculating the Reynolds number for a flow of steam in a pipe, this is the general formula I am trying to use: $$Re=\frac{\rho d v}{\mu}$$ with density $\rho$, pipe diameter $d$, flow steam $v$ ...
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1answer
37 views

Water and steam ratio

What is the relationship between the water and steam? I've read that 1 mililiter of water evaporate to 1.6 LITER of steam. Is that true?
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37 views

Modelling the diffusion of gas in a container with non uniform temperature

I want to model diffusion of a gas (e.g. water vapor diffusion in air) in a container with a temperature gradient. One side of the container has a hole, but for simplicity of boundary conditions I can ...
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1answer
35 views

On the definition of the compressibility`

The compressibility factor for a real gas can be defined in two equivalent ways, $$Z = \frac{V_{measured}}{V_{ideal}} \equiv \frac{p_mV_m}{nRT} $$ where the subscripts $m$ stand for measured ...
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21 views

Temperature Frequency relationship for gas?

I am getting something like this T (C) = Constant*log(Frequency) I do not have background of physics and I am wondering, if there is any formula which can explain the physics behind it? Something ...
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25 views

Timescales for isothermal processes

My understanding is that processes in ideal gases need to take place over relatively long timescales to be idealised as "isothermal" such that the gas temperature can be assumed not to change. For ...
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3answers
240 views

Why does the system move until equal temperatures are obtained?

In my college level thermodynamics class, the teacher gave us the example of a closed system which consisted of a box thermally insulated. A piston fully divides the box in two parts, and each is ...
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1answer
123 views

Is the Maxwell distribution a solution of the Boltzmann equation?

I am studying about the Boltzmann Equation for non equilibrium rarefied gases (dilute gases to be more specific): $$\frac{\partial f}{\partial t}+\pmb{v}\cdot\nabla_{\pmb{x}}f=Q(f,f)$$ My question is ...
3
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1answer
212 views

What happens in a gas of magnets?

This SMBC comic asks what happens if you make a gas of magnetic particles: I was wondering whether anyone has run into actual examples of this or something like it. A classical example similar to ...
3
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1answer
72 views

Thermodynamics of expanding nitrogen bubble as it rises in water

Problem An air bubble is released from a nitrogen tank 20 meters under water. The bubble has a radius of 1 mm. What will be the radius of the bubble when it reaches the surface? My Questions Is it ...
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2answers
52 views

physical meaning of pressure derivatives

Is there any physical meaning of the first and second derivatives of pressure with respect to time? If this helps, I am considering ideal gases.
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102 views

Calculating the entropy of a monatomic ideal gas

I am looking at the start of the consider how to calculate the entropy of a monatomic ideal gas. We need to determine the number of microstates in $E \leq \mathcal{H}(\Gamma) \leq E+\Delta$. The ...
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77 views

How does a heated constant volume flow behave, for an expanding flow tube leading into the free atmosphere

I have a helium gas flow with a flow rate that has been set to a constant value ($0.3\,m^3/h$). It's streaming upwards in the picture, and beyond the upper big red dot position, it meets the ...
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1answer
56 views

Is the gas constant really a constant?

For ideal gases we have $$ C_p-C_v=R $$ now the left hand side of this equation is temperature dependent, so how is it possible that gas constant $R$ is temperature independent?
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167 views

Why is most probable speed not equal to rms speed for an ideal gas?

The rms speed of ideal gas is $$\mathit{v_{rms}} = \sqrt{\dfrac{3RT}{M}}.$$ The most probable speed is the speed where $\dfrac{dP(\mathit {v})}{dv} =0$ where $P(\mathit{v})$ is the probability ...
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699 views

How fast will sublimed dry ice mix with air?

I saw this photo and wondered: Will the CO2 stay mostly in a layer on the floor with the rest of the atmosphere resting on top, or will it quickly diffuse throughout the room? This lab is probably ...
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Doubt about Hard Sphere Model

I couldn't find a proper answer about this question: if I have a gas formed by a single species (ex: biatomic gas like O2), what is the diameter $\sigma$ of the relative hard sphere model? Is it the ...