Selenium and arsenic reactions believed to take place in the flue gases of coal combustion facilities were investigated. Prior theoretical work involving various As and Se species was completed using DFT and a broad range of ab initio methods. Building upon that work, the present study is a determination of the kinetic and thermodynamic parameters of the reactions, Se + O-2 -> SeO + O and As + HCl -> AsCl + H at the CCSD/RCEP28VDZ and QCISD(T)/6-311++G(3df, 3pd) levels of theory, respectively. Transition state theory was used in determining the kinetic rate constants along with collision theory as a means of comparison. The calculated K-eq values are compared to experimental data, where available.