The adsorption of H2S on Fe(1 0 0) is examined using ab initio molecular dynamics at 298 and 1808 K. Dissociation of H2S occurs at both temperatures simulated, to leave adsorbed S and two H atoms. The dissociation occurs via a two step process and the mechanism is found to be different depending on the temperature of the reaction. At 1808 K, diffusion of the dissociated H atoms into the subsurface region is also observed.