The chemical kinetics of the Pt catalyzed oxidation reaction SO2(g) + 1/2O(2)(g) <---->(pt) SO3(g) are studied using first-principles density functional theory (DFT). The diffusion processes Of O, SO2, and SO3 are investigated in detail, revealing complex and unintuitive behavior. It is found that the self-diffusivities decrease in the order SO2, O, and SO3. For the formation Of SO3, both the Langmuir-Hinshelwood and the Eley-Rideal surface reaction steps are investigated in p(2x2) supercells, and the activation energies are found to be 46 and 25 kJ/mol, respectively. Both of these activation energies are much smaller than the SO3 desorption energy of 113 kJ/mol.