AbstractBoth nonisothermal and isothermal catalytic effectiveness factors are computed for kinetic rate laws of the Langmuir‐Hinshelwood, Hougen‐Watson type, involving surface coverage by reactant and products. Selectivity taxation is also treated and the significant influence of interphas heat and mass gradients surrounding the catalyst is displayed. The complexities of these real kinetic systems suggest caution in the use of prior generalizations based upon simpler rate l