In this paper a method is described for the validation of kinetic models in complex pyrolysis processes where n-pentane is formed. The method requires the calculation of the kinetic severity function (KSF) and the measure of the yields of different compounds in different conditions. The first condition that the calculation must fulfill is that the slope of the In(pentane yield) vs KSF graph must be logical, considering the decomposition kinetic law of the n-pentane. The method is applied to polyethylene pyrolysis in order to test the modeling previously carried out and to analyze the variations of the different yields of each compound vs KSF when the waxes are cracked.