I have been reading about carbon monoxide online. It is lighter than air; Yet, in the case of fire, most online sources claim it spreads evenly throughout a room. Why is this the case? How is it possible to model this?

  • $\begingroup$ Completely off the cuff guess, the fire gives the CO molecules kinetic energy to spread everywhere. Hope you get a better answer though. $\endgroup$ – user108787 May 25 '16 at 11:33
  • $\begingroup$ Molecular mass of CO is 28. Molecular mass of N2 (80% of air) is 28. Now, in a fire, I don't think diffusion is the largest term to consider, given all the convection and whatnot going on. $\endgroup$ – Jon Custer May 25 '16 at 12:45
  • $\begingroup$ Molecular weight of air = 29 g/mol. Molecular weight of CO = 28 g/mol. It would be more reasonable to ask why we don't observe oxigen-nitrogen stratification. And as a matter of fact, stratification is present in the atmosphere, but on much larger scales than the eight of a room... $\endgroup$ – valerio May 25 '16 at 12:52
  • $\begingroup$ @valerio92 -- That is true, but only above ~100 km above the surface. Long-lived gases are well mixed in the troposphere and stratosphere, and that includes argon (molecular weight = 40 g/mol) and CO2 (molecular weight = 44 g/mol). $\endgroup$ – David Hammen May 25 '16 at 14:57
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    $\begingroup$ Related: Why does air remain a mixture? $\endgroup$ – David Hammen May 25 '16 at 15:04

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