The reaction of forsterite with hydrogen-its apparent and real temperature dependences

We have studied experimentally the reaction rate between solid forsterite and hydrogen gas, one of the most fundamental reactions in the solar nebula. It was found that the rate-controlling gas species was atomic hydrogen rather than molecular hydrogen, from the linear dependence of the reaction rate on P_H. The temperature dependence of the reaction rate was determined both under constant P_ and under constant P_H conditions. The former, "apparent" activation energy of the reaction was estimated to be 86.5±4.8 (2σ)kcal/mol. The latter, "real" activation energy was estimated to be 32.6±4.8 (2σ)kcal/mol. From this, a general formula that gives the true reaction rate of forsterite with hydrogen was obtained : log_<10>(J_F/g cm^<-2>s^<-1>)=-32.6(±4.8)×10^3/2.303 RT+log_<10>(P_H/atm)+4.00(±0.07).