Hydrogen (H)
Hydrogen (H) is the simplest and most abundant chemical element in the universe, primarily found as a diatomic gas under standard conditions. Its atomic number is 1, and it exists in three isotopes: protium, deuterium, and tritium. Most hydrogen on Earth is found in chemical compounds, particularly water, from which it can be extracted through electrolysis or chemical reactions. Hydrogen serves as a crucial chemical reactant, notably in the Haber-Bosch process for ammonia production, and has significant potential as an energy source. It can be used in fuel cells and engines, and research into its fusion properties presents an alternative energy avenue. Despite its high energy density, hydrogen's low boiling point and explosive reactivity with oxygen pose challenges for storage and use. Historically, hydrogen was discovered by Henry Cavendish in the 18th century, and its applications have evolved, including its former use in airships before safety concerns shifted buoyancy to helium. Current advancements include producing hydrogen from renewable sources, emphasizing its role in sustainable energy development.
Hydrogen (H)
Where Found
Hydrogen is the most abundant substance in the universe and is the principal constituent of stars such as the Sun. Because of its low molecular weight, gaseous hydrogen is not retained in Earth’s atmosphere, and it must be produced by the decomposition of its chemical compounds. The principal source of hydrogen is water, from which the hydrogen must be extracted by chemical reaction or electrolysis.
Primary Uses
Hydrogen is useful both as a chemical reactant and as a source of energy. Hydrogen is used in the commercially important Haber-Bosch process for the production of ammonia. It is added to oils and fats to raise their melting points. It is also used as a fuel in certain engines and in fuel cells. The production of energy by the controlled fusion of hydrogen nuclei has been explored as an alternative to fossil and nuclear (fission) energy sources.
Technical Definition
Hydrogen (chemical symbol H), atomic number 1, is the simplest chemical element, existing under normal conditions as a diatomic gas or in chemical combination with other elements. It has three isotopes. The lightest isotope, atomic mass 1.00797, is sometimes referred to as protium to distinguish it from the much rarer deuterium, or heavy hydrogen, with atomic mass 2.014. The third isotope, tritium, with atomic mass 3.016 and a of 12.26 years, is produced in trace amounts by cosmic rays bombarding the atmosphere. Hydrogen has a melting point of -259.14° Celsius and a boiling point of -252.87° Celsius.
Description, Distribution, and Forms
Nearly all the hydrogen that exists on Earth is found in chemical combination with other elements. Since the vast majority of chemical compounds involve hydrogen, there is little point in trying to identify a separate chemistry of hydrogen. As the supply of hydrogen available is inexhaustible for all practical purposes, the main reason for including it in a discussion of natural resources is the effect of hydrogen-based technologies on the use of more limited resources.
History
Credit for the discovery of hydrogen is generally awarded to the English scientist Henry Cavendish, who collected the flammable gas released when iron and other metals reacted with acid and reported its properties in 1766. Later, English surgeon Anthony Carlisle and English chemistWilliam Nicholson made use of the newly developed voltaic pile to produce hydrogen through the electrolysis of water. Because of its inherently low density, hydrogen was used to provide buoyancy for balloons and other lighter-than-air craft, a practice that ended with the destruction by fire of the zeppelin Hindenburg in 1937. Helium replaced hydrogen for buoyancy applications.
Much research in the later third of the twentieth century was directed toward achieving hydrogen fusion under controlled conditions on Earth. The principal engineering challenge has been the containment of the extremely hot plasma necessary for sustained nuclear fusion, but at least partial success has been obtained with the tokamak, a device that uses strong magnetic fields to confine the plasma. Considerable excitement was generated within the scientific community in 1989 when two electrochemists at the University of Utah announced that they had achieved deuterium fusion by electrochemical means in a table-top apparatus. Numerous attempts were made to repeat their experiment, with disappointing results. Within a few years, most scientists had come to consider the evidence for “cold fusion” to be inconclusive at best.
Obtaining Hydrogen
Hydrogen gas may be produced by the action of an acid on a reactive metal, by the electrolysis of water, or by the reaction of water with carbon or at high temperature. Because of its small size, hydrogen can enter the lattice structure of many metallic elements. This creates a problem in steels, particularly in oil-drilling equipment, in which hydrogen embrittlement can cause mechanical failure. On the other hand, a number of transition metals, notably palladium, can absorb large quantities—up to one hydrogen atom per metal atom—of hydrogen and release it under controlled conditions, thus offering the potential for safe and compact storage of this high-energy fuel.
Uses of Hydrogen
Hydrogen is a very dense energy source in the sense that the combustion of a few grams of hydrogen in air releases a great deal of heat energy. The usefulness of hydrogen as a fuel is somewhat limited by its low boiling point and the fact that it readily forms an explosive mixture with oxygen from the air. Hydrogen tends to be used as a fuel only in situations in which weight is an overriding concern. Thus it is used to provide electrical power in spacecraft. There has been increasing interest in using hydrogen as a fuel for motor vehicles, because the only combustion product is the environmentally acceptable water. By the 2020s, some automobile companies had developed and sold hydrogen-powered vehicles. Use of hydrogen in the load leveling of power-generating systems has also been explored. In this case it would be produced by electrolysis when demand for electrical energy is low and used to power fuel cells during peak demand periods. Hydrogen can be produced from solar energy either by using photovoltaic cells to electrolyze water or directly by a photogalvanic process in which light energy absorbed by a semiconducting material is used to split the hydrogen-oxygen bond in water. Steam reacts with coal to form synthesis gas, a mixture of hydrogen, carbon monoxide, carbon dioxide, and methane that can be burned as a fuel or exposed to a catalyst to form further hydrocarbons.
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