The pyrolysis process of thermally small biomass particles was modeled combining the Lumped Capacitance Method (LCM) to describe the transient heat transfer and the Distributed Activation Energy Model (DAEM) to account for the chemical kinetics. The inverse exponential temperature increase predicted by the LCM was considered in the mathematical derivation of the DAEM, resulting in an Arrhenius equation valid to describe the evolution of the pyrolysis process under inverse exponential temperature profiles. The Arrhenius equation on which the simple LCM-DAEM model proposed is based was derived for a wide range of pyrolysis reactor temperatures, considering the chemical kinetics data of four lignocellulosic biomass species: pine wood, olive kernel, thistle flower, and corncob. The LCM-DAEM model proposed was validated by comparison to the experimental results of the pyrolysis conversion evolution of biomass samples subjected to various inverse exponential temperature increases in a TGA. To extend the validation, additional biomass samples of Chlorella Vulgaris and sewage sludge were selected due to the different composition of microalgae and sludge compared to lignocellulosic biomass. The deviations obtained between the experimental measurements in TGA and the LCM-DAEM predictions for the evolution of the pyrolysis conversion, regarding the root mean square error of temperature, are below 5 degrees C in all cases. Therefore, the simple LCM-DAEM model proposed can describe-accurately the pyrolysis-process of a thermally small biomass particle, accounting for both the transient heat transfer and the chemical kinetics by solving a simple Arrhenius equation.