Pd-based membrane reactors (MRs) are characterized by infinite H-2 selectivity of the membrane used: no other species permeates through an ideal Pd-based membrane. In a closed system consisting of two chambers the produced H, permeates from reaction side to permeate one, driving the reaction to a further conversion. The equilibrium state does not depend on kinetics, permeation law, membrane area or thickness, membrane nature, mixing degree etc. but depends only on temperature, retentate and permeate side pressures, molar feed ratio, sweep factor.