A variable-temperature scanning tunneling microscope (STM) was used to initiate and observe the abstraction of a single hydrogen atom in a simple bimolecular reaction. Dicarbon (CC) on the Cu(001) surface reacted separately with hydrogen sulfide (H2S) and water (H2O) to form CCH + SH and CCH + OH, respectively. At 9 K, hydrogen abstraction from H2O occurred spontaneously upon contact between CC and thermally diffusing H2O molecules. Hydrogen abstraction from H2S was effected at 9 K by inducing H2S diffusion via excitation with tunneling electrons. The thermal diffusion and reaction of HPS and CC were also observed at 45 K. By removing a single hydrogen atom from H2S and H2O using tunneling electrons, we established the identities of the sulfhydryl (SH) and hydroxyl (OH) reaction products. SH and OH did not react with CC under conditions that led to the reaction of the parent molecules. The bimolecular reactions H2O + O --> 2OH and H2S + O --> SH + OH did not occur thermally at 9 K but were induced by tunneling electrons.