A certain volume of argon gas ( Mol.wt = 40) requires 45 s to diffuse through a hole at a certain pressure and temperature. The same volume of another gas of unknown molecular weight requires 60 s to pass through the same hole under same conditions?

1 Answer
Sep 1, 2017

71 g/ mol

Explanation:

since kinetic energy of every gases dipends only from the absolute temperature (Ek = KT) and then at a certain temerature is equal for every gasses, and kinetic energy is also given from Ek=12mv2 you have that v^2 is proportional to the inverse of the molecular mass.
For that, the Graham's law says MbMa=V2aV2b
but speed is proportional to the inverse of the time occurred to diffuse so
Mb=Ma×t2bt2a=40gmol×602452=71gmol