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History and Production
Derive from the Greek word Hydros genes, meaning "water forming". Discovered in 1766 by H. Cavendish at London, England. Produced mainly from the catalytic steam-hydrocarbon process using natural gas or oil-refinary feedstock.
It is also produced as a byproduct of the brine elctrolysis process for the manufacture of chlorine and sodium hydroxide. It is used in large quantities in the production of ammonia (Haber process) and in the hydrogenation of fats and oils. It is also used in the reduction of metallic ores, and in a smaller quantities, as a rocket fuel and welding.
The isotope 2H or deuterium (D) is also used, in the form of heavy water (D2O), as a moderator to slow down neutrons. Hydrogen has the potential to use as alternative clean energy to replace natural gas and fossil fuel.
Physical Data
Neutral, odorless, colorless gas. Exists as diatomic molecule, H2 in room temperature. It is the most abundant of all elements in the universe, which makes up more than 90% of all the atoms.
Interatomic distance: 74.6 pm
Melting point: -259.34°C
Boiling point: -252.87°C
Thermal conductivity/Wm-1K-1: 0.1815 (27°C)
Density/kgm-3: 70.6 (-262°C), 70.8 (b.p.), 0.08988 (0°C)
Standard Thermodynamic Data (atomic gas)
Enthalpy of formation: 218 kJ/mol
Gibbs free energy of formation: 203.3 kJ/mol
Entropy: 114.7 J/mol K
Heat capacity: 20.8 J/mol K
Electronic data
Electronic configuration: 1s1
Term symbol: 2S1/2
Electron affinity: 72.7688 kJ/mol Electronegativity (Pauline): 2.20
Ionization energy (first, second, third): 1312, -, - kJ/mol
Chemical property
The chemical behavior of hydrogen resembles the Group I (alkali metals) and Group VII (halogens) elements. It combines directly with most of the elements: with metals it forms hydride (H-) anions and covalently bonded
to nonmetals (such as HCl, CH4). The properties of most acids in aqueous solutions arise from the presence of H+ ions (believed to be in combination with a water molecule to give hydroxonium ions, [H3O]+).
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