Li3N(s) + 2 H2(g) <-> LiNH2(s) + 2 LiH(s) dH° = -192 kJ/mol_rxn Because pure H2 is a hazardous subst — Kinetics Chemistry Question

Li₃N(s) + 2 H₂(g) <-> LiNH₂(s) + 2 LiH(s) dH° = -192 kJ/mol_rxn

Because pure H₂ is a hazardous substance, safer and more cost effective techniques to store it as a solid for shipping purposes have been developed. One such method is the reaction represented above, which occurs at 200°C.

Which of the following is the most likely reason that the reaction occurs at a significant rate only if the temperature of the reaction mixture is greater than 200°C?