Chem. induced hot carriers are detected with a time resoln. of 0.1 s by measuring currents in Ta/TaOx/Au tunnel junctions while the Au top electrode is exposed to at. hydrogen. Up to 3.5 nA cm-2 are measured when exposing the Au surface to a flux of 0.4 ML s-1. Comparison of the recorded current traces with modeled reaction kinetics indicates a large contribution from the Langmuir-Hinshelwood (LH) reaction. 4.5 Times larger signals are obsd. for hydrogen than for deuterium exposure. A model using the concept of electronic friction provides first insights into the structure of the induced electronic excitations.