Estimate the mean free path for a water molecule in water vapour at 373 K.

Explanation

The number density (n) is inversely proportional to absolute temperature.
`n alpha 1/T rArr (n_(373))/(n_(273))-(273)/(373)`
`rArr n_(373)=n_(273) xx (273)/(373)`
`n_(373)=2.7 xx 10^(25) xx (273)/(373)=2 xx 10^(25)m^(-3)`
Given `d=2 xx 10^(-10)m`
Hence, mean free path `lambda=(1)/(sqrt2 pi d^2 n)`
`=(1)/(sqrt2 xx 3.14 xx (2 xx 10^(-10))^(2) xx 2 xx 10^(25))=4 xx 10^(-7)m`