Based on the modified surface film renewal model

a mathematical model for the liquid phase mass transfer accompanied by a 1st-order irreversible chemical reaction is derived

i. e. A discussion of the "Chemical Method" used for the determination of inter-facial area is presented. In applying this model

k1=2 is being taken as the condition for the absorption process approaching to steady state

the concept for the time of reaction penetrating through is proposed. If the depth where the relative solute concentration be degraded to 0.01 is taken as the thickness of the reaction zone

an expression for calculating is derived. Moreover

a process for calculating the interfacial area and the frequencies of surface renewal by this model is also suggested. Based on the procedure proposed

some data taken from the literature are treated

and the results are compared with that from the Danckwerts model.