A basic requirement in the analysis of catalytic reactors is a rate expression for the reaction concerned. In the design of any equipment the equations to be used contain certain basic physical-chemical coefficients whose values must be known. In the case of physical operations, these coefficients can usually be predicted from available correlations and the design of equipment is often carried out from first principles. But there is no method available by which the kinetic rate parameters of a chemical reaction can be predicted; thus experimental determination of these parameters is unavoidable.