What are the heaviest and lightest gases at standard conditions?

Question

jfraser · Answer

By "heavy", do you mean a high mass, or dense, so a balloon filled with that gas would "sink" in air?

anonymous · Answer

Sorry, didn't explain myself very well. I meant density

jfraser · Answer

Have you learned the ideal gas law yet? If you have, you can manipulate it to solve for ratios like density (mass/volume) and the answer should appear from that.

kainui · Answer

The heaviest and lightest gases at standard temperature and pressure are simply going to be the ones with more volume than others. As for density, the density of all gases at standard temperature and pressure is the same!

jfraser · Answer

@Kainui, you are incorrect. Under identical conditions, the volume of different gasses is the same for all gasses, but since every gas has a different mass, the densities will all be different.
$$PV=nRT$$ so $$P/RT = n/V$$since$$n = mass (g)/MM$$ then
$$P*MM/RT = g/V$$g/V is the density, so we have
$$D  =MM*P/RT$$ so the density of different gases under identical conditions of pressure and temperature will be directly proportional to the molar mass. The densest gas will be the one with the highest molar mass.

kainui · Answer

Yeah, I honestly don't know what I was thinking there haha. This is why you shouldn't just trust what people say on the internet and should also look at other sources like google and wikipedia!

anonymous · Answer

Thanks for the answers. The thing I don't know now is what is the heaviest gaseous substance at standard conditions

unklerhaukus · Answer

Well Hydrogen gas has got to be the lightest,
And as for pure elements i guess Radon would be heaviest

anonymous · Answer

Thanks Unkle, but I need to know the heaviest molecule, not elemental gas.
As for hydrogen, it really has got to be the lightest.