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

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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
25 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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1answer
39 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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20 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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0answers
19 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
25 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
70 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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1answer
23 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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3answers
369 views

Conversion of ideal gas to real gas via $Z$ compression factor

The ideal gas equation $PV=nRT$ can be converted into real gas equation by compression factor $Z$ i.e $PV=Z~ nRT)$. My question is what is $Z$ and how does it arise? Is $PV/nRT$ a compression ratio of ...
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2answers
44 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
14 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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1answer
22 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 ...
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4answers
15k views

Why does a gas get hot when suddenly compressed? What is happening at the molecular level?

My guess is that the molecules of gas all have the same speed as before, but now there are much more collisions per unit area onto the thermometer, thus making the thermometer read a higher ...
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3answers
172 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
47 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
262 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 ...
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2answers
228 views

$E=kT$ or $\frac32kT$?

Basically, which is the correct formula for thermal energy, and is this the same as kinetic energy? My notes are pretty conflicting on this topic, and I'm getting pretty confused.
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1answer
32 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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0answers
31 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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2answers
40 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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22 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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2answers
66 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
45 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
49 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 ...
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31 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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2answers
11k views

Calculating work done on an ideal gas

I am trying to calculate the work done on an ideal gas in a piston set up where temperature is kept constant. I am given the volume, pressure and temperature. I know from Boyle's law that volume is ...
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1answer
20 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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30 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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19 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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31 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
28 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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0answers
16 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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0answers
21 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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1answer
4k views

Calculate mass of air in a tyre from pressure

How can one calculate the mass of air inside a tyre, given a particular tyre size; a pressure, in $kPa = \frac{1000kg}{m\cdot s^2}$; and assuming room temperature, and normal air composition? I can't ...
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228 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
114 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 ...
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2answers
6k views

Work Done by an Adiabatic Expansion

I am given the information that a parcel of air expands adiabatically (no exchange of heat between parcel and its surroundings) to five times its original volume, and its initial temperature is 20° C. ...
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199 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 ...
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1answer
86 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 ...
3
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1answer
60 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
46 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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71 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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2answers
118 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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1answer
52 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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694 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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17 views

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 ...
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1answer
35 views

What assumptions can be made using a $pV$ diagram?

In this question I am asked to find the volume of a gas at $V_3$ I have some parts that am not clear on. Is it reasonable to assume the temperature at $3$ is $657^{\circ}C$ Work is done by the ...
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2answers
793 views

How does a gas of particles with uniform speed reach the Maxwell-Boltzmann distribution?

Take an empty container and fill it with $N$ gas particles (ideally a monoatomic gas), each having the same kinetic energy $E$, then isolate the container. Since initially the speeds don't follow the ...
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1answer
51 views

Decrease in system pressure do to gas dissolution?

A system of fixed volume contains two fluids as illustrated in the figure below, in equal volumes. Their pressures are both equal and high (much greater than atmospheric pressure). Initially the ...
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3answers
837 views

Temperature change inside pressure chamber

Let's say there is a pressure chamber with some sort of sample / specimen (e.g. protein crystal) in it. Now I apply a certain amount of gas pressure, e.g. 10 or 20 atm. Let's say I use xenon as a gas. ...