In this paper the equations modeling absorption accompanied by a zero order reaction and by a pseudo-zero order reaction in the liquid phase are analytically solved by using the film theory. For the cases of both zero and pseudo-zero order reaction the analysis leads to conclusion that three regimes of the process need to be considered; the three corresponding reactant concentration profiles are developed : for low values of the Hatta number (Ha), the reaction does not go to completion in the liquid film, and therefore the reactant concentration in the liquid bulk is not zero; for intermediate values of Ha, the concentration becomes zero at the film-bulk interface, but its gradient is not zero so that an instantaneous reactant consumption takes place at such interface; for higher values of Ha the reactant concentration becomes zero in the liquid film. The dependence of the enhancement factor on Ha is also determined, allowing the description of transition from the slow reaction regime to the fast and instantaneous reaction regime.