How does molecular hydrogen split into individual hydrogen atoms?

A molecule of hydrogen ($H_2$) dissociates into two individual atoms when it is supplied with energy equal to or greater than its dissociation energy, which is 104 kcal/mole. This process breaks the chemical bond holding the atoms together.1

Sufficient energy to trigger this dissociation can be provided through several methods, such as:

• Contact with a white-hot tungsten filament.1
• Establishing an electric discharge within the gas.1

Once dissociated, atomic hydrogen is highly reactive and will readily combine with most elements to form hydrides or reduce metallic oxides. If this process occurs at low pressure, the resulting hydrogen atoms can maintain a significant lifetime before recombining. Conversely, certain metal surfaces, such as platinum, can catalyze the recombination of these atoms back into molecules, a process that releases energy and heats the metal to incandescence.1