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Dihydrogen – Structure, Properties and Applications

  • Last Updated : 18 Nov, 2021

The lightest element is hydrogen. Under normal conditions, hydrogen is a gas composed of diatomic molecules with the formula H2. It is colourless, odourless, non-toxic, and extremely flammable. Hydrogen is the most abundant chemical element in the universe, accounting for roughly 75% of all normal matter. Stars, such as the Sun, are mostly made up of hydrogen in its plasma state. The majority of hydrogen on Earth is found in molecular forms such as water and organic compounds.

The chemical element hydrogen has the symbol H and the atomic number 1.

Dihydrogen

Dihydrogen is a homonuclear diatomic molecule made up of two hydrogen atoms. This molecule has a covalent bond between two hydrogen atoms, which fulfils each of their duet configurations. Dihydrogen is the lightest known molecule because hydrogen is the lightest element on the modern periodic table. Under normal temperature and pressure conditions, dihydrogen exists as a colourless, tasteless, and odourless gas that is highly combustible in nature. 

H2 is the molecular formula for dihydrogen.

Structure of Dihydrogen

The dihydrogen molecule is made up of two hydrogen atoms that are joined together by a single covalent bond. This molecule is nonpolar and has a linear shape. One electron is contributed to the covalent bond by each hydrogen atom. As a result, the duet configuration requirements of both hydrogen atoms in the dihydrogen molecule are met.

Properties of Dihydrogen

  • Dihydrogen exists in the gaseous state at STP.
  • The melting point is 14 Kelvin.
  • On the Kelvin scale, the boiling point of dihydrogen is 20.3 Kelvin.
  • The H2 molecule’s latent heat of fusion corresponds to 0.12 kilojoules per mole.
  • Dihydrogen has a latent heat of vaporization of 0.904 kilojoules per mole.
  • H2 has a molar heat capacity of approximately 28.83 joules per mole Kelvin.
  • When sound travels through gaseous H2, its speed is 1310 metres per second.

Applications of Dihydrogen

Large amounts of H2 are required on a regular basis in the chemical and petroleum industries. Dihydrogen is primarily used in the refining of certain fossil fuels as well as the production of ammonia. The petrochemical industry is a major consumer of H2. In this business, dihydrogen is employed in processes including hydrodesulfurization, hydrodealkylation, and hydrocracking.

This compound, for example, can be used as a hydrogenating agent, particularly to increase the saturation level of unsaturated fats and oils. This compound is also used in the production of methanol. Similarly, dihydrogen is used as a hydrogen source in the production of hydrochloric acid. H2 is also a reducing agent and can thus be used to treat metallic ores.

Biochemistry of Dihydrogen: It is not uncommon for dihydrogen to be produced as a byproduct of anaerobic metabolism. Many microorganisms produce this compound as well, usually through chemical reactions catalyzed by enzymes. Hydrogenases are enzymes that catalyze biochemical reactions involving the release of dihydrogen and are known to contain iron or nickel.

Dihydrogen as a fuel

Dihydrogen has a wide range of applications, including electrochemical cells, which produce more energy than diesel and gasoline. As a result, scientists have coined the term Hydrogen Economy, with the goal of utilizing low-carbon energy sources. This gas is highly efficient and relatively inexpensive when compared to other energy sources.

The calorific value and heat output of hydrogen is extremely high. Its high heating value provides a higher ignition temperature and a longer flame sustaining time. Since dihydrogen is abundant, it can be used as a fuel that is highly economical for commercial use. A fuel cell functions similarly to a battery in that it generates electricity through an electrochemical reaction. A hydrogen fuel cell is an electrochemical cell that uses a spontaneous redox reaction to generate workable current. Exothermic is the overall reaction. When the two half-cell potentials for the electrochemical reaction are added together, the result is a positive cell potential.

At Anode:                                                                                                  H2 → 2H+ + 2e



At Cathode:                                                                                        12O2 + 2H+ + 2e→ H2O

Hydrogen Economy

John Bockris coined the term hydrogen economy during a 1970 talk. J.B.S. Haldane, a geneticist, first proposed the idea.

The hydrogen economy employs hydrogen to decarbonize economic sectors that are difficult to electrify. Hydrogen can be made from water using sustainable energy sources like wind and solar, and its combustion produces only water vapour, allowing us to phase out fossil fuels while reducing climate impact.

Hydrogen is a powerful fuel that is frequently used as rocket fuel, but numerous technical challenges prevent the development of a large-scale hydrogen economy. These include the difficulty of developing long-term storage, pipelines, and engine equipment; a relative lack of off-the-shelf engine technology that can currently run safely on hydrogen; safety concerns about the high reactivity of hydrogen fuel with oxygen in ambient air; the high cost of producing it through electrolysis; and a lack of efficient photochemical water-splitting technology. Hydrogen can also react in a fuel cell, which efficiently generates electricity in a process that is the inverse of water electrolysis. 

Nonetheless, the hydrogen economy is slowly emerging as a minor component of the low-carbon economy. Hydrogen is currently primarily used as an industrial feedstock, primarily in the production of ammonia and methanol, as well as in petroleum refining. In recent years, more discoveries of naturally occurring hydrogen in continental, on-shore geological environments have been made, paving the way for the novel field of natural or native hydrogen, which will aid in energy transition efforts.

In today’s hydrocarbon economy, natural gas is used primarily for heating, and petroleum is used for transportation. The combustion of hydrocarbon fuels produces carbon dioxide and other pollutants. The demand for energy is increasing, and hydrogen can be a more environmentally friendly source of energy for end-users, releasing no pollutants such as particulates or carbon dioxide.

Hydrogen has a high energy density in terms of weight but a low energy density in terms of volume. Even when highly compressed, solidified, or liquified, the energy density by volume is only 1/4 that of gasoline, despite the fact that the energy density by weight is approximately three times that of gasoline or natural gas. Hydrogen has the potential to transport and store renewable energy over long distances, such as wind power or solar electricity, and thus help to decarbonize long-distance transportation, chemicals, and iron and steel.

Sample Questions 

Question 1: What is the type of bond in dihydrogen?

Answer:

The dihydrogen molecule is made up of two hydrogen atoms that are joined together by a single covalent bond.



Question 2: What is the shape of a dihydrogen molecule?

Answer:

The dihydrogen molecule has a linear shape and is nonpolar.

Question 3: Why can dihydrogen be used as a fuel?

Answer:

The calorific value and heat output of hydrogen are extremely high. Its high heating value provides a higher ignition temperature and a longer flame sustaining time. Because dihydrogen is abundant, it can be used as a fuel that is highly economical for commercial use.

Question 4: What is hydrogen economy?

Answer:

The hydrogen economy employs hydrogen to decarbonize economic sectors that are difficult to electrify. Hydrogen can be made from water using sustainable energy sources like wind and solar, and its combustion produces only water vapour, allowing us to phase out fossil fuels while reducing climate impact.

Question 5: Which is the lightest known molecule?

Answer:

Dihydrogen is the lightest known molecule.


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