![]() It combines with most elements to form hydrides ( e.g., sodium hydride, NaH), and it reduces metallic oxides, a reaction that produces the metal in its elemental state. If atomic hydrogen is generated in a system at low pressure, the atoms will have a significant lifetime- e.g., 0.3 second at a pressure of 0.5 millimetre of mercury. Sufficient energy is obtained, for example, when the gas is brought into contact with a white-hot tungsten filament or when an electric discharge is established in the gas. The dissociation energy of molecular hydrogen is 104,000 calories per mole-written 104 kcal/mole (mole: the molecular weight expressed in grams, which is two grams in the case of hydrogen). One molecule of hydrogen dissociates into two atoms (H 2 → 2H) when an energy equal to or greater than the dissociation energy ( i.e., the amount of energy required to break the bond that holds together the atoms in the molecule) is supplied. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today. ![]()
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