The elementary irreversible gas reaction A$($g$)+$ B$($g$)>$C$($g$,$l$)$ is carried out isothermally in a PFR in which pressure drop is negligible. As the reaction proceeds the partial prossure of $C$ builds up until a point is reached at which $C$ begins to condense when vapor pressure of $C$ is $0\mathrm{.}4$atm. For an equal molar feed of $A+B$ with no inerts and no other species entering the system, determine reaction rate at the onset of condensation.

Given, CAO $0\mathrm{.}02mo\frac{l}{d}m3$

Total pressure at entrance $-2$ atm