Quantitative description of the catalytic process carried out in an isothermal fluidized-bed was presented. The expansion or contraction of gas, often disregarded, has been taken into account. The influence of nonequimolarity of a chemical process on the hydrodynamics of the fluidized bed and degrees of conversion of reactants was analyzed. The influence of various simplifications on the accuracy of the model was also discussed. The results obtained showed strong connection between chemical reaction stoichiometry and the hydrodynamics of the medium in which the reaction occurs.