10In earlier work, a fundamental mathematical model was proposed for side-blowing operation in the 11 argon-oxygen decarburization (AOD) process. The purpose of this work is to present a new model, 12 which focuses on the reactions during top-blowing in the AOD process. The model considers 13 chemical reaction rate phenomena between the gas jet and the steel bath as well as between the gas 14 jet and metal droplets. The rate expressions were formulated according to a law of mass action based 15 method, which accounts for the mass transfer resistances in the liquid metal, gas and slag phases. The 16 generation rate of the metal droplets was related to the blowing number theory. This paper presents 17 the description of the model, while validation and preliminary results are presented in the second part 18 of this work. 19 20