Diffusion accompanied by instantaneous chemical reactions in a multicomponent drop is modeled. The developed model is then simulated for the case of absorption of one solute from a continuous phase into the drop, followed by fast reactions with two different reactants existing in the drop. The results of the model are obtained by using Galerkin’s finite element method and represented by unsteady concentration profiles of all components in the drop, the reaction front positions, and the cumulative mass flux and the enhancement factor of the diffusing solute. The effects of the system parameters, such as diffusivities of the solute and the reactants, the relative amount of the reactants in the drop, and the interfacial concentration of the solute, on the calculated quantities are evaluated.