Consider the chemical vapor deposition $($CVD$)$ process for the manufacture of solid silicon thin films as illustrated below. A dilute mixture of $0\mathrm{.}1$mol$\%$ silane, $Si{H}_4($species A$),$ in $H_2$ gas $($species B$)$ enters the chamber and flows over a square $Si$ wafer of $15cm$ per side at a bulk velocity of $50c\frac{m}{s}.$ At the surface of the Si wafer, the following reaction takes place:

$Si{H}_4(g)Si(s)+2H_2(g)$