Combustion
Hydrogen gas (dihydrogen or molecular hydrogen) is highly flammable:
2 H2(g) + O2(g) → 2 H2O(l) + 572 kJ (286 kJ/mol)
The

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Discovery and use
In 1671, Robert Boyle discovered and described the reaction between iron filings and dilute

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Hydrogen, as atomic H, is the most abundant chemical element in the universe, making up 75 percent of normal matter by massand more than 90 percent by number of atoms. (Most of the

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H 2 is produced in chemistry and biology laboratories, often as a by-product of other reactions; in industry for the hydrogenation of unsaturated substrates; and in nature as a means of expelling reducing equivalents in biochemical reactions.
Electrolysis of water

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H2 is a product of some types of anaerobic metabolism and is produced by several microorganisms, usually via reactions catalyzed by iron- or nickel-containing enzymes

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Hydrogen poses a number of hazards to human safety, from potential detonations and fires when mixed with air to being an asphyxiantin

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Petrochemical industry
Large quantities of H 2 are used in the "upgrading" of fossil fuels. Key consumers of H 2 include hydrodealkylation, hydrodesulfurization, and hydrocracking. Many of these reactions can be classified as

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