lhydrogène

Lhydrogène is the chemical element hydrogen, symbol H, and atomic number 1. It is the lightest element and the most abundant in the universe by mass, present mainly in stars and gas giants. On Earth, hydrogen is mostly bound in water and organic compounds; free hydrogen gas occurs in small quantities in certain geologic and atmospheric contexts.

Under standard conditions, hydrogen exists as a diatomic molecule, H2. It is colorless, odorless, and highly flammable, with a very low density, causing it to rise rapidly when released and to require careful containment.

Industrial production includes steam methane reforming and electrolysis of water. Green hydrogen uses renewable electricity; blue hydrogen uses reforming with carbon capture; grey hydrogen uses reforming without capture. Storage and transport face challenges due to low energy density by volume; solutions include compression, liquefaction, or chemical/storage media.

Major applications are as a feedstock for ammonia synthesis, petroleum refining, and energy storage via fuel cells. Hydrogen is used as a rocket propellant and is considered a potential clean energy carrier for transportation and power systems, depending on production method and lifecycle emissions.

Isotopes include protium, deuterium, and tritium. Discovered by Henry Cavendish in 1766 and named by Antoine Lavoisier, hydrogen has a long history in chemistry. Safety considerations center on flammability and the risk of explosive mixtures with air.