Hmm…is there a gas which is significantly more viscous than the ballpark range of values in which most gas falls?
Wait…I should add some qualification: Let’s assume with Temp held constant around room temp, say 60 F.
Well, Jinx, you didn’t mention pressure, so you should know that there are phase diagram solutions for gases that are indistinguishable from liquids. All you need to do is find a gas whose critical temperature is below 60 degrees Farenheit and voila!, you’ve got an arbitrarily viscous gas as you increase pressure to infinity.
The Most Viscous Gas?
Man! If I eat onion rings from Burger King… about 6 hours later. Wow! That’s some viscious gas!! :eek:
[sup]Oh… wait…[/sup]
Here, lemme hijack slightly for Jinx. What’s the most viscous gas at STP?
I’m assuming that fog is considered a suspension of water molecules in air, and is not considered water vapor.
Still, water vapor is pretty viscous at STP … but at STP it is just liquid water. Does the OP mean “How viscous can a gas get before being considered a liquid state?”
Doesn’t sodium sublimate at a fairly low temperature?
According to this site, radon is the heaviest known gas, and is a gas at room temperature. Wouldn’t heavy = viscous?
Yes. Temperature increases with the average kinetic energy of the molecules in matter; at a given temperature, all gases will therefore have the same average kinetic energy. Because KE is 1/2 * mv[sup]2[/sup], the heaviest molecules will move most slowly. For a gas, that’s pretty much all there is to viscosity.
The noble gases are listed in the CRC Handbook of Chemistry and Physics as the highest-viscosity gases, their viscosity increasing with molecular weight. Neon is the highest on the list, over 300 micropoise at 20ºC, but radon is not listed; I would expect it to be more viscous than neon.
Bordelond, radon is the heaviest element which is a gas at STP. Most of us, however, live in a world where compounds rather than native elements are the principal constituents of matter. And just without research, I can note Uranium Hexafluoride as being a heavier and presumably more viscous gas than Radon. (Actually UF[sub]6[/sub] is a liquid which boils at a temperature only slightly above STP.)
I’d suggest organic chemistry as a fertile source for finding the possible answers; I recall ethylene as gaseous at STP, and am confident there are other, denser and presumably more viscous organic gases.
Fraid not. Metals enjoy staying as solids except for Mercury.
I’m pretty sure radon is the heaviest gas even when you take into consideration molecular gases. At 222 amu, you would need 18.5 carbon atoms or about 14 oxygen atoms to equal the atomic weight. Organic molecules with that many constituents are not gases. For example, ethylene has an atomic weight of a paltry 26 amu. You’re just not going to be able to get a compound that’s as non-self-attractive as radon with those kinds of masses per particle.
Uranium hexafluoride is a good candidate, but it certainly isn’t a gas at 60 Fahrenheit.
What about that stuff used in Halon fire supressant systems? (I’m not sure if Halon is the name of the gas, or the system itself). It’s supposed to be a gas, and yet many times heavier than air.
Halon-1301 has a molecular weight of of only 150 amu or so.
I’m thinking of the solid-sodium-meets-water experiment. Never mind me.
:o
Leafing through the CRC handbook I found Perfluorobutane (C[sub]4[/sub]F[sub]10[/sub]), with molecular weight 238 and boiling point 3.96°C. There are probably some other heavy fluorinated alkanes around.
(This doesn’t answer the OP; I have no idea how viscous it is.)
That’s a good one, Omphaloskeptic. We might also try perchlorobutane which I imagine will have a similarly low boiling point.
A couple interesting points I dredged up:
In this web page a formula for viscosity in a gas is derived:
Visc = 5(MRT/[symbol]p[/symbol])[sup]1/2[/sup]/(16N[sub]A[/sub][symbol]s[/symbol][sup]2[/sup])
where M is molecular weight, R is the gas constant, T is temperature, N[sub]A[/sub] is Avagadro’s number, and [symbol]s[/symbol] is the collision diameter of the molecule. As they point out, this means that viscosity is dependent on temperature, but not on pressure.
More importantly, the highest-viscosity gas should be the one that combines high molecular weight and low collision diameter (and note that viscosity is much more sensitive to the diameter than the weight!).
Also, from here: perfluorobutane viscosity (25C) = 0.01454 cP.
From my CRC, some viscosities:
Air (18C) 0.01827 cP
Oxygen (19C) 0.02018 cP
Helium (20C) 0.01941 cP
Neon (20C) 0.03111 cP
Argon (20C) 0.02217 cP
Krypton (15C) 0.0246 cP
Xenon (20C) 0.02260 cP
I hypothesize that organic compounds like perfluorobutane, although heavier, have a large enough collision diameter that the actual viscosity is pretty low. Furthermore, I suggest that neon might be about as viscous a gas as you can get. Note, though, that the viscosity of neon is less than twice that of air, say, so it’s not like there’s a huge jump in viscosity.
Thanks zut. It would seem to be that because viscosity is due to a shear stress and not a normal stress there is no dependency upon pressure.
If you ionized your gas, I imagine your collision diameter would drop dramatically. Of course, then you technically aren’t dealing with a gas but a plasma.