How can high temperatures help hydrogen react with metals to form hydrides?

High temperatures facilitate the formation of metallic hydrides by overcoming the significant energy barrier required to initiate reactions with molecular hydrogen. At room temperature, the reaction rates between hydrogen gas and most metals are negligible, largely due to the high dissociation energy (104 kcal/mole) required to break the bond holding the hydrogen atoms together in a molecule.1

By applying heat, the kinetic energy of the system increases, allowing the hydrogen molecule to dissociate into reactive atomic hydrogen or simply increasing the reaction rate to a measurable level. Once dissociated, this atomic hydrogen is highly reactive and can combine with various transition metals, as well as lanthanoid and actinoid series metals, to form hard, alloy-like interstitial hydrides. In these processes, the metal's crystal lattice typically expands to accommodate the hydrogen atoms. For example, the preparation of uranium hydride requires heating to 300 °C (570 °F) to drive the reaction between uranium and hydrogen gas.12