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It is the lightest element and, at standard conditions, is a gas of diatomic molecules with the formula H 2, sometimes called dihydrogen, [11] but more commonly called hydrogen gas, molecular hydrogen or simply hydrogen.
High pressure electrolysis is the electrolysis of water by decomposition of water (H 2 O) into oxygen (O 2) and hydrogen gas (H 2) by means of an electric current being passed through the water. The difference with a standard electrolyzer is the compressed hydrogen output around 120–200 bar (1740–2900 psi, 12–20 MPa). [146]
Liquid hydrogen (H 2 (l)) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H 2 form. [4] To exist as a liquid, H 2 must be cooled below its critical point of 33 K. However, for it to be in a fully liquid state at atmospheric pressure, H 2 needs to be cooled to 20.28 K (−252.87 °C; −423.17 °F). [5]
Hydrogen (1 H) has three naturally occurring isotopes: 1 H, 2 H, and 3 H. 1 H and 2 H are stable, while 3 H has a half-life of 12.32(2) years. [3] [nb 1] Heavier isotopes also exist; all are synthetic and have a half-life of less than 1 zeptosecond (10 −21 s). [4] [5] Of these, 5 H is the least stable, while 7 H is the most.
Proton: 1 H + (i.e. the cation of protium) Deuteron: 2 H +, D + Triton: 3 H +, T + In addition, the ions produced by the reaction of these cations with water as well as their hydrates are called hydrogen ions: Hydronium ion: H 3 O + Zundel cation: H 5 O 2 + (named for Georg Zundel) Eigen cation: H 9 O 4 + (or H 3 O + •3H 2 O) (named for ...
This is the ratio found in the gas giant planets, such as Jupiter. The analysis of deuterium–protium ratios (2 H 1 HR) in comets found results very similar to the mean ratio in Earth's oceans (156 atoms of deuterium per 10 6 hydrogen atoms). This reinforces theories that much of Earth's ocean water is of cometary origin.
Within one of these phases, the gas is usually considered isothermal, except near an expanding H II region. [3] Near an expanding H II region is a dense HI region, separated from the undisturbed HI region by a shock front and from the H II region by an ionization front. [3]
The formula for acyclic saturated hydrocarbons (i.e., alkanes) is C n H 2n+2. [1]: 623 The most general form of saturated hydrocarbons, (whether linear or branched species, and whether with or without one or more rings) is C n H 2n+2(1-r), where r is the number of rings. Those with exactly one ring are the cycloalkanes.