Dihydrogen: Definition, Diagram, Formula and Examples

Dihydrogen

Edited By Shivani Poonia | Updated on Jul 02, 2025 06:10 PM IST

Dihydrogen is the more common name for hydrogen, which is a substance becoming the most basic of all chemical elements. Numerous applications are going to the most diverse fields of sciences and industries. It fuels rockets other than in the periodic table to send people living into orbit and on the other side of the ground, it more and more fuels clean energies. Versatility and important position in parameters regarding industry and environmental control underline the ways for its production through steam reforming of natural gas and electrolysis of water.

This Story also Contains

Physical Properties of Hydrogen
Chemical Properties of Hydrogen
Uses of Hydrogen
Ortho and Para hydrogens:
Some Solved Examples
Summary

Dihydrogen

Preparation of Dihydrogen

Preparation of Hydrogen: There are a number of methods for preparing dihydrogen from metals and metal hydrides.

Laboratory Method
- It is usually prepared by the reaction of granulated zinc with dilute hydrochloric acid.
  Zn + 2H⁺ → Zn²⁺ + H₂
- It can also be prepared by the reaction of zinc with aqueous alkali.
  Zn + 2NaOH → Na₂ZnO₂ + H₂
Commercial preparation method
- The electrolysis of acidified water using platinum electrodes gives hydrogen.
  [1]
  Cathode Reaction
  2H++2e→H2
  Anode Reaction
  H2O−2e−→2H++1/2O2
  Hydrogen gas is formed at the cathode while Oxygen is formed at the anode.
  Twice as much Hydrogen as Oxygen is formed.
- It is obtained as a byproduct in the manufacture of sodium hydroxide and chlorine by the electrolysis of brine solution. During electrolysis, the reactions that take place are:
- At Anode: 2Cl−→Cl2+2e−
  At cathode : 2H2O(l)+2e−→H2( g)+2OH−(aq)
  Overall reaction is
  2Na+(aq)+2Cl−(aq)+2H2O(l)→Cl2(g)+H2(g)+2Na+(aq)+2OH−(aq)
- High purity (>99.95%) dihydrogen is obtained by electrolyzing warm aqueous barium hydroxide solution between nickel electrodes.
- By the reaction of Zn with aqueous alkali: Hydrogen can also be prepared by the reaction of zinc with aqueous alkali.
  Zn(s) Zinc +2NaOH(aq) Sodium hydroxide → Heat Na2ZnO2(aq)+H2(g)↑ Sodium zincate Hydrogen Zn(s)+ dil. 2HCl(aq) Hydrochloric acid ⟶ZnCl2(aq) Zinc chloride +H2( g)↑ (dil.)
- Water Gas: The reaction of steam on hydrocarbons or coke at high temperatures in the presence of a catalyst yields hydrogen.
  CnH2n+2+nH2O→Ni1270 KnCO+(2n+1)H2
  The mixture of CO and H₂is called water gas. As this mixture of CO and H₂ is used for the synthesis of methanol and a number of hydrocarbons, it is also called synthesis gas or 'syngas'.
  The process of producing 'syngas' from coal is called 'coal gasification.
  C+H2O→1270 KCO+H2
- Water Gas Shift Reaction: The production of dihydrogen can be increased by reacting carbon monoxide of syngas mixtures with steam in the presence of iron chromate as a catalyst.
  CO(g)+H2O(g)673 K catalyst CO2( g)+H2( g)
  This is called the water-gas shift reaction.

Physical Properties of Hydrogen

Physical Properties of Hydrogen: Dihydrogen is a colorless, odorless, tasteless, combustible gas. It is lighter than air and insoluble in water. The electronegativity of hydrogen is in between metals and non-metals so it behaves as both electropositive and electronegative.

Disadvantage: A leak not only means a loss of hydrogen but is, in addition, a decided hazard because of the inflammability and very wide explosive limits that hydrogen possesses. These limits are much wider than for most gases.

The list of physical properties of Hydrogen and its isotopes are mentioned in the table below:

H-H bond Enthalpy: The H–H bond dissociation enthalpy is the highest for a single bond between two atoms of any element. It is because of this factor that the dissociation of dihydrogen into its atoms is only ~0.081% around 2000K which increases to 95.5% at 5000K. Also, it is relatively inert at room temperature due to the high H–H bond enthalpy.

Chemical Properties of Hydrogen

Chemical Properties of Dihydrogen: Dihydrogen accomplishes reactions by

(i) loss of the only electron to give H⁺

(ii) gain of an electron to form H^–

(iii) sharing electrons to form a single covalent bond.

The chemistry of dihydrogen can be illustrated by the following reactions:

Reaction with halogens: It reacts with halogens, X₂ to give hydrogen halides, HX.

H2(g)+X2(g)→2HX(g)(X=F,Cl,Br,I)

Reaction with dinitrogen: With dinitrogen, it forms ammonia.

3H2( g)+N2( g)→Fe673 K,200 atm2NH3( g);ΔH⊖=−92.6kjmol−1

This is the method for the manufacture of ammonia by the Haber process.

Reaction with dioxygen: It reacts with dioxygen to form water. The reaction is highly exothermic.

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2H2( g)+O2( g)→2H2O(ℓ)ΔH∘=−285.9KJ/mol

Reactions with metals: Many metals, combine at a high temperature to yield the corresponding hydrides
H2( g)+2M(g)→2MH(s) where M is an alkali metal
Hydrogen reacts with many organic compounds in the presence of catalysts to give useful hydrogenated products of commercial importance. For example :
Hydrogenation of vegetable oils using nickel as a catalyst gives edible fats (margarine and vanaspati ghee)
Hydroformylation of olefins yields aldehydes which further undergo reduction to give alcohols.

H2+RCH2CH2CHO→RCH2CH2CH2OH

H2+CO+RCH=CH2→RCH2CH2CHO

Uses of Hydrogen

The various uses of dihydrogen are as follows:

The largest single use of dihydrogen is in the synthesis of ammonia which is used in the manufacture of nitric acid and nitrogenous fertilizers.
Dihydrogen is used in the manufacture of vanaspati fat by the hydrogenation of polyunsaturated vegetable oils like soybean, cotton seeds, etc.
It is used in the manufacture of bulk organic chemicals, particularly methanol.CO(g)+2H2( g)→ coalt CH3OH(l)
It is widely used for the manufacture of metal hydrides.
It is used for the preparation of hydrogen chloride, a highly useful chemical.
In metallurgical processes, it is used to reduce heavy metal oxides to metals.
It is used as rocket fuel in space research.
Dihydrogen is used in fuel cells for generating electrical energy. It has many advantages over conventional fossil fuels and electric power. Fuel cells generate power by establishing a potential difference between the two electrodes.
Hydrogen produces more energy than fossil fuels.

Ortho and Para hydrogens:

In a molecule of hydrogen when the spin of both H-atoms is in the same direction, they are known as ortho hydrogen.

In a molecule of hydrogen when the spin of both H-atoms is in the opposite direction, they are known as para-hydrogen.

Some Solved Examples

Example 1:

Question:
Calculate the volume of hydrogen gas produced at STP when 10 grams of zinc reacts with excess dilute sulfuric acid.

Solution:
- Moles of zinc = \( \frac{10 \text{ g}}{65.38 \text{ g/mol}} = 0.153 \text{ mol} \)
- Volume of hydrogen gas at STP = \( 0.153 \text{ mol} \times 22.4 \text{ L/mol} = 3.43 \text{ L} \)

Example 2:

Question:
If 5.6 grams of water is electrolyzed using platinum electrodes, calculate the volume of oxygen gas produced at STP.

Solution:
- Moles of water = \( \frac{5.6 \text{ g}}{18.015 \text{ g/mol}} = 0.311 \text{ mol} \)
- Moles of oxygen gas = \( 0.5 \times 0.311 \text{ mol} = 0.156 \text{ mol} \)
- Volume of oxygen gas at STP = \( 0.156 \text{ mol} \times 22.4 \text{ L/mol} = 3.50 \text{ L} \)

These examples demonstrate how to calculate the volume of gases produced in chemical reactions and electrolysis experiments using simple stoichiometry and gas laws.

Summary

The importance of hydrogen goes beyond just being an element. Its influence ranges from the roots of chemistry to the most modern of applications among boundaries of science, industry, and the environment. In showing its potential, hydrogen will play a key role in moving sustainable technologies forward and overcoming global challenges.

Frequently Asked Questions (FAQs)

1. 1. How is hydrogen mainly produced?

Hydrogen mainly comes from the steam reforming of natural gas and electrolysis of water where, through chemical reactions, the liberalization of hydrogen gas happens.

2. 2. How does hydrogen contribute to clean energy?

Hydrogen fuels fuel cells in electrical vehicles and can be made from renewable resources, thus creating a clean alternative to fossil fuels.

3. 3. What are Ortho and Para Hydrogen, and why are they important?

Ortho and Para hydrogen represent nuclear spin isomers of hydrogen that, at very low temperatures, show different properties. These properties make them very important in precise spectroscopy or when involved in cryogenic applications.

4. 4. What are some of the significant chemical reactions of Hydrogen?

Hydrogen reacts in basic industrial processes with oxygen to form water and nitrogen to produce ammonia.

5. 5. What are the environmental benefits of hydrogen?

Hydrogen can be derived from renewable sources and, when fed into fuel cells, will give a minimal amount of emission of greenhouse gases and thus provide a clean source of energy.

6. How does the electron configuration of hydrogen lead to H2 formation?

Hydrogen has one electron in its outermost shell. To achieve a stable electron configuration, hydrogen atoms share their electrons, forming a covalent bond. This results in the H2 molecule, where both atoms achieve a stable "full" outer shell similar to helium.

7. Can H2 form hydrogen bonds?

No, H2 molecules cannot form hydrogen bonds with each other. Hydrogen bonding requires a hydrogen atom bonded to a highly electronegative atom (like N, O, or F). In H2, the electrons are shared equally between the two hydrogen atoms, so there's no partial charge separation needed for hydrogen bonding.

8. Why is H2 considered a reducing agent?

H2 is a strong reducing agent because it can easily donate its electrons to other substances. When H2 reacts, it often splits into two H+ ions, each releasing an electron. This ability to provide electrons makes it effective at reducing other compounds, especially metal oxides.

9. How does the reactivity of H2 compare to atomic hydrogen?

Atomic hydrogen (H) is much more reactive than molecular hydrogen (H2). This is because breaking the strong H-H bond in H2 requires significant energy. Once this bond is broken, the individual H atoms are highly reactive due to their unpaired electron and desire to achieve a stable electron configuration.

10. What is dihydrogen and why is it called that?

Dihydrogen is the chemical name for molecular hydrogen (H2). It's called "di-hydrogen" because each molecule contains two hydrogen atoms bonded together. This naming convention helps distinguish it from atomic hydrogen (H), which exists as single atoms.

11. What is ortho-hydrogen and para-hydrogen?

Ortho-hydrogen and para-hydrogen are two forms of H2 that differ in their nuclear spin states. In ortho-H2, the spins of the two nuclei are parallel, while in para-H2, they're antiparallel. At room temperature, normal H2 is about 75% ortho and 25% para. The ratio changes at very low temperatures, affecting properties like heat capacity.

12. How does quantum tunneling affect H2?

Quantum tunneling significantly affects H2 due to the small mass of hydrogen atoms. This phenomenon allows H2 molecules to pass through barriers they classically shouldn't be able to overcome. Quantum tunneling contributes to H2's behavior at low temperatures and plays a role in certain chemical reactions involving H2.

13. How does the specific heat capacity of H2 compare to other gases?

H2 has the highest specific heat capacity of any gas. This means it can absorb or release more heat per unit mass for a given temperature change compared to other gases. This property makes H2 useful in some cooling applications but can also present challenges in its storage and use.

14. How does H2 contribute to the formation of stars?

H2 plays a crucial role in star formation. In molecular clouds, H2 can radiate away excess heat, allowing the cloud to collapse under gravity. As the cloud collapses and heats up, H2 molecules dissociate, and eventually, the hydrogen atoms undergo nuclear fusion, marking the birth of a star.

15. What is the difference between hydrogen and deuterium?

Deuterium is an isotope of hydrogen. While a normal hydrogen atom (protium) has one proton and no neutrons in its nucleus, deuterium has one proton and one neutron. This gives deuterium twice the mass of protium, affecting properties like boiling point and reaction rates. D2 (deuterium gas) behaves similarly to H2 but with some distinct differences.

16. Why is H2 a gas at room temperature?

H2 is a gas at room temperature because of its weak intermolecular forces. The small size of H2 molecules and their non-polar nature result in very weak van der Waals forces between molecules. This allows them to move freely as a gas under normal conditions.

17. How does the bond in H2 compare to other diatomic molecules?

The H-H bond in H2 is one of the strongest single bonds known. It's shorter and stronger than bonds in other diatomic molecules like N2 or O2. This is because the small size of hydrogen atoms allows for significant orbital overlap, resulting in a strong covalent bond.

18. How does the density of H2 compare to air?

H2 is much less dense than air. At standard temperature and pressure, H2 has about 1/14th the density of air. This is why hydrogen balloons and airships rise - the buoyant force from displacing heavier air is greater than the weight of the hydrogen.

19. How does H2 behave under high pressure?

Under very high pressures, H2 can exhibit unusual behaviors. As pressure increases, H2 can transition from a gas to a liquid, and at extremely high pressures, it can even become metallic. This metallic form of hydrogen is predicted to be a superconductor and is of great interest in physics and planetary science.

20. Why doesn't H2 have a dipole moment?

H2 doesn't have a dipole moment because it's a homonuclear diatomic molecule. The two hydrogen atoms share electrons equally, resulting in a symmetrical distribution of charge. There's no separation of positive and negative charges within the molecule, so there's no net dipole.

21. How does H2 contribute to the concept of a "hydrogen economy"?

In a hydrogen economy, H2 would serve as a primary energy carrier, similar to electricity today. H2 can be produced from renewable sources, stored, and then used in fuel cells to generate electricity or directly as a fuel. This system could potentially provide clean, sustainable energy with water as the only byproduct.

22. Why is H2 considered a potential "clean" fuel?

H2 is considered a clean fuel because when it's used in a fuel cell or combusted, the only product is water vapor. Unlike fossil fuels, it doesn't produce CO2 or other pollutants during use. However, the overall environmental impact depends on how the H2 is produced.

23. What is the significance of H2 in organic chemistry?

In organic chemistry, H2 is crucial for hydrogenation reactions. These reactions add hydrogen atoms to unsaturated compounds, often using metal catalysts. This process is important in industrial chemistry, for example in the production of margarine from vegetable oils or in the synthesis of many pharmaceuticals.

24. What safety concerns are associated with H2 use?

The main safety concerns with H2 are its high flammability and potential for explosion when mixed with air. H2 has a wide range of flammable concentrations in air (4-75% by volume) and requires very little energy to ignite. It can also leak easily due to its small molecule size, requiring special storage and handling procedures.

25. What role does H2 play in the universe?

H2 is the most abundant molecule in the universe. It plays a crucial role in star formation, serving as fuel for nuclear fusion in stars. In interstellar space, H2 can form on the surface of dust grains and is a key component of molecular clouds, the birthplaces of stars.

26. How does H2 interact with metals?

Many metals can absorb H2, a process called hydrogen embrittlement. H2 molecules dissociate at the metal surface, and the atoms can diffuse into the metal lattice. This can cause structural changes and weaken the metal. However, this property is also useful for hydrogen storage in certain metal hydrides.

27. How does the boiling point of H2 compare to other gases?

H2 has an extremely low boiling point of about -252.9°C (-423.2°F) at standard pressure. This is the second-lowest boiling point of any substance (only helium is lower). The low boiling point is due to the weak intermolecular forces between H2 molecules.

28. What role does H2 play in the Earth's atmosphere?

H2 is present in trace amounts in Earth's atmosphere (about 0.5 parts per million by volume). It's primarily produced by human activities and certain microorganisms. H2 doesn't significantly contribute to atmospheric chemistry due to its low reactivity, but it can escape into space due to its low molecular weight.

29. How is H2 typically produced industrially?

The main industrial method for H2 production is steam reforming of natural gas. This process reacts methane with high-temperature steam in the presence of a catalyst to produce H2 and CO2. Other methods include electrolysis of water, coal gasification, and biomass processing.

30. What is the difference between "green", "blue", and "grey" hydrogen?

These terms refer to the production method of H2. "Green" hydrogen is produced using renewable energy sources. "Blue" hydrogen is made from fossil fuels, but the CO2 produced is captured and stored. "Grey" hydrogen is produced from fossil fuels without capturing the CO2 emissions.

31. How does H2 behave in fuel cells?

In a fuel cell, H2 is split into protons and electrons at the anode. The protons pass through a membrane to the cathode, while the electrons flow through an external circuit, generating electricity. At the cathode, the protons and electrons combine with oxygen to form water.

32. Why is H2 sometimes called an "energy carrier" rather than an energy source?

H2 is called an energy carrier because it's not a primary energy source like fossil fuels or solar energy. Instead, it's a way to store and transport energy. Energy from other sources is used to produce H2, which can then be used to generate electricity or power vehicles.

33. What is meant by the "hydrogen economy"?

The "hydrogen economy" refers to a proposed system where hydrogen is used as the primary medium for energy storage and transport. In this scenario, H2 would be produced from renewable sources, distributed, and used in fuel cells or combustion engines to generate power, with water as the only byproduct.

34. How does H2 interact with light?

H2 doesn't absorb visible light, which is why it's colorless. However, it does interact with light in other parts of the electromagnetic spectrum. H2 has distinct absorption and emission spectra in the ultraviolet and infrared regions, which are useful for its detection and study, particularly in astronomical observations.

35. What is the significance of H2 in the early universe?

H2 played a crucial role in the early universe. After the Big Bang, as the universe cooled, H2 was one of the first molecules to form. Its ability to cool through rotational and vibrational transitions was essential for the formation of the first stars and galaxies, as it allowed matter to collapse under gravity.

36. How does the bond energy of H2 compare to other diatomic molecules?

The H-H bond in H2 is one of the strongest single bonds known, with a bond energy of about 436 kJ/mol. This is higher than most other diatomic molecules. For comparison, the N-N bond in N2 is about 945 kJ/mol (triple bond), while the O=O bond in O2 is about 498 kJ/mol (double bond).

37. What is the significance of H2 in biochemistry?

While H2 itself isn't commonly found in biological systems, hydrogen plays crucial roles in many biochemical processes. Some microorganisms can use H2 as an energy source or produce it as a byproduct. H2 is also being studied for potential therapeutic applications due to its antioxidant properties.

38. How does temperature affect the properties of H2?

Temperature significantly affects H2 properties. As temperature increases, H2 molecules move faster, increasing pressure in a closed container. At very high temperatures, H2 molecules can dissociate into atomic hydrogen. At low temperatures, quantum effects become more pronounced, affecting properties like specific heat.

39. What is the relationship between H2 and plasma?

At very high temperatures, H2 can form a plasma state where the molecules are dissociated into a mix of electrons and protons. This hydrogen plasma is the most common state of matter in the universe, found in stars. Understanding hydrogen plasma is crucial for fusion energy research.

40. How does H2 behave in extreme gravitational fields?

In extreme gravitational fields, like those near neutron stars or black holes, H2 behaves unusually. The intense gravity can cause the electron clouds of H2 molecules to deform. In some theoretical models, H2 might even form chain-like structures under these extreme conditions.

41. What is the significance of the H2 molecule in quantum mechanics?

The H2 molecule is the simplest multi-electron system and plays a crucial role in quantum mechanics. It's often used as a model system for understanding molecular bonding, electron correlation, and quantum chemical calculations. The study of H2 has been fundamental in developing quantum mechanical theories of molecular structure.

42. How does H2 contribute to the concept of "chemical potential"?

H2 is often used as a reference point in discussions of chemical potential, particularly in electrochemistry. The standard hydrogen electrode, based on the H+/H2 redox couple, is defined as having a potential of 0 volts. This provides a universal reference for measuring the potentials of other electrochemical reactions.

43. What is the role of H2 in interstellar chemistry?

H2 is a key player in interstellar chemistry. It can form on the surface of dust grains and participate in various reactions. Many interstellar molecules are formed through reactions involving H2. The presence of H2 also affects the temperature and dynamics of interstellar clouds, influencing star formation processes.

44. How does H2 behave under cryogenic conditions?

At cryogenic temperatures, H2 exhibits unique behaviors. As it approaches its boiling point (-252.9°C), quantum effects become more pronounced. The ortho-para ratio changes, affecting properties like heat capacity. At even lower temperatures, H2 can form a quantum solid, where zero-point motion plays a significant role.

45. What is the significance of H2 in planetary atmospheres?

H2 is a major component of the atmospheres of gas giant planets like Jupiter and Saturn. It contributes to their weather patterns and energy transport. The presence or absence of H2 in a planet's atmosphere can provide clues about the planet's history, current conditions, and potential for hosting life.

46. How does H2 interact with carbon to form hydrocarbons?

H2 can react with carbon under certain conditions to form hydrocarbons. This process, known as hydrogenation, is important in both natural processes (like the formation of natural gas) and industrial applications (like coal liquefaction). The reaction typically requires high temperatures, pressures, and often catalysts.

47. What is the role of H2 in the water-gas shift reaction?

In the water-gas shift reaction, H2O reacts with CO to produce H2 and CO2. This reaction is important in many industrial processes, including hydrogen production and syngas processing. H2 is both a product and can influence the equilibrium of this reversible reaction.

48. How does H2 contribute to the concept of "proton conductivity"?

H2 plays an indirect but crucial role in proton conductivity. When H2 dissociates, it can form protons (H+ ions) which can move through certain materials. This proton conductivity is essential in fuel cells, where H2 is oxidized to protons at the anode, and these protons then travel through a membrane to the cathode.

49. What is the significance of H2 in nuclear fusion research?

H2, particularly its isotopes deuterium and tritium, is central to nuclear fusion research. The fusion of deuterium and tritium nuclei is the most promising reaction for controlled fusion energy. Understanding the behavior of hydrogen isotopes under extreme conditions is crucial for developing fusion reactors.

50. How does H2 storage pose challenges for its use as a fuel?

Storing H2 efficiently is a major challenge for its use as a fuel. Due to its low density, large volumes are needed to store significant amounts of energy. Options include high-pressure tanks, cryogenic liquid storage, and chemical storage in metal hydrides. Each method has trade-offs in terms of energy density, cost, and safety.

51. What is the role of H2 in the Haber-Bosch process?

H2 is a key reactant in the Haber-Bosch process, which is used to produce ammonia (NH3). In this process, H2 reacts with N2 under high temperature and pressure in the presence of a catalyst. This reaction is crucial for the production of fertilizers and has had a significant impact on global agriculture.

52. How does H2 contribute to the greenhouse effect?

Unlike CO2 or methane, H2 itself is not a greenhouse gas as it doesn't absorb infrared radiation. However, H2 can indirectly affect climate by influencing the concentrations of other greenhouse gases. For example, H2 can react with hydroxyl radicals in the atmosphere,