We have used density functional theory along with the cluster approximation to investigate the adsorption of chlorinated silanes on the Si(100)-2 x 1 surface. We have calculated the energetics for various adsorption reactions. We found that dissociative adsorption of chlorosilanes via scission of either the Si-H or Si-Cl bond is exothermic by 50-53 kcal/mol. The vibrational frequencies of the adsorption products were also calculated. It was found that the calculated frequencies for the dissociative adsorption of SiH2Cl2, SiHCl3, and SiCl4 via Si-CI scission are in good agreement with experiments. Transition state barriers were calculated for adsorption via scission of the Si-Cl bond and via scission of the Si-H bond. We find that the barrier for SiH2Cl2 and SiHCl3 adsorption via scission of the Si-Cl bond is 6-9 kcal/mol lower than the barrier for adsorption via scission of the Si-H bond. This indicates that the reaction pathway is kinetically controlled. Furthermore, the adsorption barrier of SiH2Cl2 is 7 kcal/mol lower than the barrier for SiH4 adsorption, This difference in barrier heights partially explains the experimental observation that SiH2Cl2 has a higher initial sticking coefficient than SiH4.