We investigate theoretically. by quantum DFT calculations, the adsorption of H-2 molecules on the [100] MoS2 surfaces, considering various edge sulfur stoichiometrics. Depending on the nature of the gas phase, the adsorption energies vary from strongly positive values to strongly negative ones. Using these energies, we have constructed a thermodynamic diagram, which gives the stoichiometry of the edges and the nature of, partial pressure ratio and the adsorbed hydrogen atoms as a function of the total pressure and of the PH2S/PH2 determines the best conditions to examine the S-H groups using spectroscopic techniques.