The adsorption of chlorine and desorption of chlorosilanes from chlorine-covered Si(111) and Cu/Si surfaces have been studied. The latter include annealed "5 x 5" Cu2Si thin films as well as room-temperature deposited copper films, on Si(111). Techniques employed include low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and temperature-programmed desorption (TPD). A Langmuir adsorption mechanism was observed for Cl on the Si(111) 7 x 7 surface, but a mobile precursor mediated process was observed for L adsorption on the Cu/Si surfaces. Chlorine-exposed Si(111) 7 x 7 surfaces yield TPD peaks of SiCl2 at similar to650 degreesC with second-order desorption kinetics. For Cu-containing surfaces, similar TPD peaks were observed at slightly lower temperatures and with different desorption kinetics. The desorption rate includes a dependence on Cl-free sites. The presence of Cu on Si(111) also led to the appearance of two additional low-temperature TPD peaks. at 200 degreesC arid 300 degreesC, both consisting of SiCl4 and SiCl2 species. We propose that the lower temperature desorption occurs through the formation of an activated SiCl2 precursor on the copper-containing surface.