The two-dimensional transition-metal dichalcogenide molybdenum disulfide (MoS2) has been intensely studied in the past several years due to its exceptional electronic, optical, and chemical properties in a wide range of applications. The chemical functionalization of MoS2 allows its properties and interfacial interactions to be tuned and controlled. Recently, we reported the direct covalent functionalization of semiconducting MoS2 with aryl diazonium salts, without the use of harsh initial treatments or phase engineering. In this paper, we confirm and expand the covalent functionalization reaction model by performing a detailed study of the reaction kinetics for monolayer MoS2 functionalized by 4-nitrobenzene tetrafluoroborate (4-NBD). We find that both the Freundlich and Temkin isotherm models are good descriptors of the reaction due to the energetically inhomogeneous surface of MoS2 and the indirect adsorbate-adsorbate interactions from previously attached nitrophenyl groups, respectively. The reaction kinetics was then found to be well described using a pseudo-second-order model, showing that the order of this reaction is two. This study supports our previous work and gives us a deeper understanding of the nature of the covalent functionalization of MoS2.