gas mixing?

[YT2095]

I think this belongs in Physics?

 

I have a 1 litre gas jar full of hydrogen gas at room temp and pressure, I then displace half of it with 500ml of CO2 gas.

so now I have a 50/50 mix of H2 and CO2.

initially because I was careful the H2 is all the top and the CO2 is at the bottom because it much denser than the H2.

 

now I give the jar a good shake and flip it end over end a few times to make it mixed well.

 

Now, will it Stay mixed, or will the H2 go to the top again and the CO2 down to the bottom?

 

like Oil and Water.

[insane_alien]

you'll probably have a higher concentration of CO2 at the bottom and H2 at the top but they won't fully separate. it'll be roughly even i would imagine since its a small container.

[YT2095]

so container size is important then?

 

btw, the question is purely Hypothetical, I haven`t actually done this, it`s just to illustrate the question.

[timo]

The height is important since the density of the two gases depends on the height via [math] \rho (h) =\alpha \exp (-mgh/kT) [/math], where [math] \rho (h) [/math] is the density, m the mass of the molecule, g the gravitational constant (if your container is soooo huge that g significantly changes, the term would probably become slightly more complicated), k the Boltzman constant, T the termperature, h height above container bottom and [math] \alpha [/math] some constant to make physical unit and total number of particles fit. As you might guess, the different masses of the two types of molecules make the function [math] \rho (h) [/math] behave differently. This results in different concentrations of the gases for different heights (the higher, the more share of the lighter gas). To find out to what extend this different concentration is measurable, you have to plug in values and check it out.

 

EDIT AND SIDENOTE: Well, the question is about physics. I suppose the chemicists use this kind of physics (thermodynamics) at least as often as physicists, so the thread would have fit in there, too. Here, I'm not sure if "General Physics" or "Classical Physics" is more appropriate.

[Comandante]

I thought that 2 gasses in container would exert exactly the same pressure on the inside of the container. Say you have gas x and gas y, if total inside pressure is 50kPa, then both x and y exert 50kPa. Initially I thought otherwise (25 and 25), but then I got it marked wrong in the test, this was chemical kinetics question, where x and y gasses were products of decomposition reaction (this was actually decomposition of [math]N_2O_2[/math]) in the same vessel, and the total pressure of each individual gas was the same as the other. I still don't know why this is the case. Perhaps this example of yours YT can help illustrate.

[YT2095]

well the Real reason behind my question is this, I have a bottle of Helium and Air mix, I wondered if I`de get more helium if I took the gas from the top and less if I inverted the bottle.

 

I used H2 and CO2 as Extreme examples of Light and Heavy.

[richard]

I would expect it to seperate.

[insane_alien]

it wouldn't seperate completely. in a 1 litre container it can probably be viewed as a homogenous mixture.if it was a million litres then there would be some degree of separation. i don't think you would be able to get full separation unless there was sufficient pressure for the CO2 to solidify.

[John Cuthber]

When I was at school we were taught that one of the poperties of a gas was that it filled the container it was placed in.

The He hardly knows about the CO2 so it will fill the container. So will the CO2. It would be a challenge to measure the difference in concentration with any sensible size of container.

You have got the equation; why not use it and see what the answer is.

[chilehed]

Even if you didn't shake the container at all, each specie would diffuse throughout the volume so that they would end up fully mixed. Left alone, they will remain fully mixed.