The performance of the gradient-corrected BLYP density functional and the hybrid B3LYP functional has been studied in calculations of bond energies of Si-H-Cl containing molecules involved in thermal chemical vapor deposition processes of silicon. Calculated atomization energies using the BLYP and BSLYP functionals are in better agreement with experiment (typically within 10 kcal/mol) compared to more computationally demanding methods such as MP4. Comparisons are also made with more accurate theoretical methods including corrected MP4 approaches. While predictions of thermochemical properties for second-row compounds from BLYP or B3LYP approaches are slightly less accurate than for first-row compounds, these techniques still represent a promising approach of obtaining theoretical estimates for thermochemical properties.