The realization of reactions in microchannel reactors demands apart from optimal process conditions also a useful geometric layout of the apparatus. Information about the usefulness of the geometry is available through the simulation of the concentrations and the temperature field and their evaluation. Although the mesopores used in microchannel reactors are very regular, the discrepancies between channel and pore dimensions are very large and so, a simultaneous numerical calculation of the entire reactor is neither meaningful nor possible. Therefore, in this paper, an effective kinetics for isothermal reactions considering the diffusional mass flow through the pore mouth is introduced. Still, numerical calculations are very expensive and have the disadvantage that the influence of the individual parameters is seen only by a lot of calculations with changed parameters. That's why a survey of cases with analytical solutions and with Other concepts (using mass transfer coefficients, effectiveness factors, etc.) is given, too.