Problem

A sphere of aaphthalene having a nadius of $2\mathrm{.}0mm$ is suspended in a large volume of still air at $318K$ and $1\mathrm{.}101325{10}^{5}Pa(1$ atm$).$ The diffusivity of the naphthalene at $318K$ is $6\mathrm{.}92{10}^{-6}\frac{m^2}{s}.$ Calculate the rate of evaporation of naphthaleae from the surface.