Can You See a Dense Patch of Gas?

[pivoxa15]

Someone said that gases are invisible. But if you confine "lots" of gas into a small encloser so that on average a gas molecule will bump into another gas molecule by traveling a distance that liquide molecules tend to bump into each other than would one be able to see this extremely dense patch of gas in this small container?

 

[Mk]

It depends on what gas. Some are colored, some are not. Also, "Raleigh scattering," and things like that can affect the color.

http://en.wikipedia.org/wiki/Raleigh_scattering

But if you confine "lots" of gas into a small encloser so that on average a gas molecule will bump into another gas molecule by traveling a distance that liquide molecules tend to bump into each other than would one be able to see this extremely dense patch of gas in this small container?

That would be... a liquid. Some are colored, some not, etc...

I think I understand your thinking now. About how sparsely-placed the gas atoms are, and that affecting color.

I think the gas still has a color, its just too weak to be seen by the human eye.

What color is hydrogen?
Helium? Liquid helium is blue right?

Can somebody show me pictures of differnet liquified gases (i've seen N2)

 

[rachmaninoff]

Helium? Liquid helium is blue right?

Liquid oxygen is blue. Hydrogen, Helium, Nitrogen, and Argon are colorless.

A nice photo of oxygen at:
http://www.rsbs.anu.edu.au/ResearchGroups/PBE/Oxygen/O2_Home.htm

 

[maverick6664]

Color by Rayleigh scattering is due to particles in the air, isn't it? And the size of particles determines the color.

But actually some gases have colors. For example, ozone is light blue, though oxygen is colorless in the gas form. see http://www.ozoneapplications.com/info/ozone_properties.htm.

 

[pivoxa15]

That would be... a liquid. Some are colored, some not, etc...

N2)

Why is my example a liquid? The particles in my small enclosed area are gas because they are above the temperture that the particles exist as liquids. In the case of H2O, the container might have a temperture of 120 celsius so they cannot be liquid because it is above H2O's boiling temperture.

So my question is "Is it possible to see gasous particles?"

The atomsphere is only made up of particles in their gasous form and we are able to see that the atomsphere is blue so does that answer my question? I am doubtful because I am not sure if the atomsphere is 100% made up of gas particles and my question is more about seeing the colour of one particular gas rather than many different gases mixed together as that of the atomsphere.

 

[Danger]

Keep in mind, pivoxa, that the state of the substance depends upon its pressure. In order to restrict the molecular motion of a gas to that of a liquid, you would have to compress it to the point that it becomes a liquid regardless of its temperature.

 

[pivoxa15]

Keep in mind, pivoxa, that the state of the substance depends upon its pressure. In order to restrict the molecular motion of a gas to that of a liquid, you would have to compress it to the point that it becomes a liquid regardless of its temperature.

So you are basically saying that if I restrict a gas so that I am able to see it, it will not be a gas anymore but a liquid. Therefore, no matter what I do, I will never be able to see the colour of particles in true gas form?

What about the atomsphere?

 

[Mk]

So you are basically saying that if I restrict a gas so that I am able to see it, it will not be a gas anymore but a liquid. Therefore, no matter what I do, I will never be able to see the colour of particles in true gas form?

Some gasses are colored, some are not. If the gas is clear, and its liquid form is colored, if you squeeze the gas, it will be a liquid. Then it will be colored. If the gas is colorless, but the liquid is not, it has no color until its sqeezed into a liquid.

 

[Danger]

So you are basically saying that if I restrict a gas so that I am able to see it, it will not be a gas anymore but a liquid. Therefore, no matter what I do, I will never be able to see the colour of particles in true gas form?

No, that's not what I meant. There are some gasses that you can see while they're still in gaseous form, although this might be a matter of definition in which I'm wrong. When they're electrically excited, you can certainly see neon, argon, xenon, etc..

What about the atomsphere?

I'm once again uncertain as to how this is defined. All of the individual gaseous components of the atmosphere are colourless. They collectively scatter the blue section of the EM spectrum, though, so the sky appears blue. I don't know anything about optics, and therefore am uncertain as to what 'colour' really means in these two instances.

 

[pivoxa15]

Some gasses are colored,

Could you name some of those colored gases and provide a reason as to why they are colored (in other words why are those gases visible)?

 

[Homer Simpson]

Many vapours are visible and have colour. Vapours are gasses (just defined as ones that will revert back to liquid readily), you can check out web definitions of the two.

Check out:
http://www.Newton.dep.anl.gov/askasci/chem03/chem03001.htm

I think that for most things we consider gasses (that are only liquified under extreme pressure or cold) the molecules/atoms are just way to far apart to provide any 'vapour colour'

 

[Tide]

We can clearly see the gases comprising the atmospheres of the gas giants in our Solar System.

 

[Danger]

Right. Never thought of that.

 

[Mk]

http://en.wikipedia.org/wiki/Image:Fog-laser.jpg
http://en.wikipedia.org/wiki/Image:Dry_ice.jpg

 

[Homer Simpson]

Bromine vapour pic on left side of screen

http://www.schoolscience.co.uk/content/3/chemistry/materials/match2pg1.html

 

[maverick6664]

But aren't fog and vapor like matter from dry ice many small drops of water/ice like smoke? So they aren't real gas.

 

[pivoxa15]

http://en.wikipedia.org/wiki/Image:Dry_ice.jpg

This picture seem to illustrate liquid vapour hence not gas.


I wonder if visible smoke from a cigarrette is classfied as a gas.

 

[Mk]

But aren't fog and vapor like matter from dry ice many small drops of water/ice like smoke? So they aren't real gas.

This picture seem to illustrate liquid vapour hence not gas.
I wonder if visible smoke from a cigarrette is classfied as a gas.

Well, you both seem to be thinking the same thing. Its kind of iffy I guess. Look at the table at http://en.wikipedia.org/wiki/Colloid What do you think? You could look at it like, its a liquid aerosol, but you could ask yourself if a bucket of paint is a liquid or not.

 

[maverick6664]

Yeah, we are thinking of the same thing. Smoke is a dense group of particles nearly the size of wavelengths of light, so no wonder it is visible and has color. And coloid is similar, except that in coloid, the size of each particle is larger than the wavelength of light.

And now I'm wondering what makes the color of gas or even liquid. Molecules (1/10 - some nano meters) are usually much smaller than wavelength of light (some hundred nano meters.) So molecule itself won't affect color.

So what makes the color of gas or liquid? I guess some color should be related to transition of energy states of electron in the atom (for ex, solution of blue vitriol, because copper compound usually has blue or green color)... Can the color of gas/liquid be explained only by transition of energy states of electron (absorbed or emitted)?

 

[pivoxa15]

When I first post this question, I was really asking whether any gases can be seen normally (not excited). I assume that this question has been answered from the example of we being able to see the atomsphere as blue. But could it be that the blueness only comes from the liquid vapour that exists in the atomsphere? Hence we are not truly able to see the pure gas in the sky?
But apparently most if not all gases are visible if you excite them such as shown http://en.wikipedia.org/wiki/Neon_sign

 

[maverick6664]

My understanding about blue sky, I think it's due to small particles (dusts or whatever) in the air, reflecting light of shorter wavelengths. (or it may be the color of the air itself..I am not sure.)

Wave reflects on objects greater than the wavelength, whilest it goes though objects smaller than the wavelength.

So, at the same time, red sunset glow is also due to the same small particles in the air, through which only the light of longer wavelengths comes to the ground. At sunset (or sunrise), the sun is low and its light comes through "thick" air, so the longer wavelength has advantage. I'm sure of this one.

 

[HallsofIvy]

Bromine vapour pic on left side of screen
http://www.schoolscience.co.uk/content/3/chemistry/materials/match2pg1.html

But vapour is not gas. Vapour is liquid droplets suspended in air.

 

[Vixus]

I'm sure gases are visible. They would be needed in large concentrations though. Isn't it all to do with which colours of light are absorbed and which aren't?

 

[Homer Simpson]

But vapour is not gas. Vapour is liquid droplets suspended in air.

That’s not true. From thermodynamics look at a temperature/enthalpy diagram.
http://www.spiraxsarco.com/learn/modules/2_15_01.asp
Water, for ex, can be liquid (technically subcooled). Add heat and you will move from a subcooled liquid to a saturated liquid (the point where any more heat addition is simply going to change phase instead of raise temp.) As you add more heat there is a region of mixed phase, part liquid, part vapour. Once enough heat is added you reach a ‘saturated vapour’ Any more heat it becomes a ‘superheated vapour’ as its temp rises again. When does water become a gas in this explanation? The point is that the vapour is a gas, and vice-versa. Its just that most things we call gas are SO far into the superheat region that you aren’t going to see it condense on your lawn some chilly night.

So what makes the color of gas or liquid?

I got wondering about the same thing, and found this on the net (dont know if it is right or not) the energy transition they talk about is not the same as exciting a gas like neon.

http://www.Newton.dep.anl.gov/askasci/chem03/chem03001.htm
Color occurs when there is an electronic
transition in a molecule whose energy difference corresponds to
wavelengths in the visible part of the electromagnetic spectrum (400-700
nm). That has nothing to do with the physical state of the substance (gas,
liquid, solid). In some cases the absorption is weak, e.g. O2 so the color
is not readily seen.

 

[Homer Simpson]

Quote:
Originally Posted by Mk
http://en.wikipedia.org/wiki/Image:Dry_ice.jpg


This picture seem to illustrate liquid vapour hence not gas.

Dry Ice fog: Gas CO2 is clear and colourless. The fog in this case is indeed liquid water drops in the air (or even possibly frozen solid water). As far as I understand, the reason it happens is the same as a cloud forming in the sky. The air temp is lowered by the dry ice to the point that the air can no longer hold its water vapour, (excess vapour). The vapour needs to condense out, so any dust in the air will provide the surface (nuclei) for this to happen. This is what you see as a cloud in this case.

Saying that, I guess the sublimation of CO2 from solid to gas would be totally invisible if it were taking place in an atmosphere of 0 humidity.

 

[pivoxa15]

Color occurs when there is an electronic
transition in a molecule whose energy difference corresponds to
wavelengths in the visible part of the electromagnetic spectrum (400-700
nm). That has nothing to do with the physical state of the substance (gas,
liquid, solid). In some cases the absorption is weak, e.g. O2 so the color
is not readily seen.

That is interesting maybe some of our classical ideas of things being visible are not accurate. The above statement leads me to think about QED although I don't know anything about it other than that it can predict all known phenomena in optics to very high precision.

So the reason why solids and liquids are easier to see is because it is easier to excite these atoms because they are fixed while it is harder to excite pure gas because they are moving around at too high speeds in order for the right amount of photon energy to excite them?

However the gases in the atomsphere are so numerous and the photons that hit it are so many and pure (since these photons come directly from the sun) that it is possible to on average excite enough gases for the gases to "spit" out enough photons for our eyes to detect.

 

[Integral]

Chlorine gas is green.

A lot depends on what you mean by "visible" . Visibility often is defined by a change in index of refraction. You "see" a shimmering of the light over hot surfaces as the index of refraction of air depends on the temperature. Light changes path when it encounters a surface. A surface is visible if there is a change in index of refraction.

There are some plastics which have the same index of refraction as some oils. If you immerse a block of plastic in a oil bath with the same index of refraction it will vanish.

 

[Homer Simpson]

If you immerse a block of plastic in a oil bath with the same index of refraction it will vanish.

Well where does it go??

 

[Mk]

The A-team took care of it.

 

[Danger]

Well where does it go??

It doesn't go anywhere; it simply can't be seen any longer. Something like sonar or just touching it will reveal that it's still there. It's just like the done-to-death movie trick of hiding diamonds in an ice-cube tray. Think of it, if you like, as perfect camouflage.