Estimate the mean free path for a water molecule in water vapour at 373 K. Given diameter of water molecule `= 2 Å` and number density of water molecule (at NTP) `= 2.7 xx 10^(25) m^(-3)`. Compare it with interatomic distance for water `= 40 Å`.

Explanation

The number density (n) is inversely proportional to absolute temperature
`therefore na(1)/(T)rArr(n_(373))/(n_(273))=(273)/(373)rArrn_(373)=n_(273)xx(273)/(373)`
`n_(373)=2.7xx10^(25)xx(273)/(373)=2xx10^(25)m^(-3)`
Given `d=2xx10^(-10)m`, Hence, mean free path
`lambda=(1)/(sqrt(2)pid^(2)n)=2.81xx10^(-7)m`