First-stage mercury oxidation reactions typical of coal combustion flue gases were investigated. The present study is a determination of the kinetic and thermodynamic parameters of the bimolecular reactions, Hg + Cl-2 <-> HgCl + Cl, Hg + HCl <-> HgCl + H, and Hg + HOCl <-> HgCl + OH, at the B3LYP/RCEP60 VDZ level of theory over a temperature range of 298.15 to 2000 K at atmospheric pressure. Conventional transition state theory was used to predict the forward and reverse rate constants for each reaction and ab initio based equilibrium constant expressions were calculated as a function of temperature. Reasonable agreement was achieved between the calculated equilibrium constants and the available experimental values.