The reaction of Cl-2 with GaAs(110) is studied with soft x-ray photoelectron spectroscopy (SXPS). The temperature dependence of the surface product distribution, in the range of 300-650 K, is derived from SXPS core-level and valence-band spectra and compared to known gas-phase product distributions. It is found that both Ga and As chlorides are formed at room temperature. Following reaction at temperatures above similar to 400K, no Cl remains on the surface. Instead, for temperatures up to similar to 600 K an As overlayer is formed, whereas reaction at similar to 650 K leads to the stoichiometric removal of Ga and As. These findings indicate that there is a direct correlation between the surface and gas-phase product distributions.