Why does molecular hydrogen usually react slowly at room temperature?

Molecular hydrogen ($H_2$) typically reacts slowly at room temperature because of its very high dissociation energy. To participate in many chemical reactions, the strong bond holding the two hydrogen atoms together must be broken, a process that requires 104 kcal/mole.1

At room temperature, there is generally insufficient energy available to overcome this high activation energy barrier, leading to negligible reaction rates. While molecular hydrogen is capable of reacting with many elements and compounds, these processes typically require elevated temperatures, sparks, radiation, or the presence of a catalyst to proceed at a measurable or rapid pace.12