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Dihydrogen-Introduction, Position in The Periodic Table, Preparation, Physical and Chemical properties, Uses, Practice Problems, FAQs

Dihydrogen-Introduction, Position in The Periodic Table, Preparation, Physical and Chemical properties, Uses, Practice Problems, FAQs

Do you know what element is most prevalent in the cosmos? You all might be surprised by the response.

Actually, it's "Hydrogen." Hydrogen, which makes up more than 90% of all atoms and accounts for around 75% of the universe's mass, received its name from the Greek words hydro, which means "water," and genes, which means "creating." is found in stars and makes up three-quarters of the universe's mass.

In many different situations, hydrogen is employed as fuel. Because it is flammable, hydrogen makes a fantastic rocket fuel. Since hydrogen emits only water as an emission, it has the potential to be a very clean form of fuel. However, pure hydrogen may be highly expensive to utilise and is very difficult to come by. Although hydrogen is flammable, gasoline is still far more flammable than hydrogen. Thermonuclear energy would be a vastly more effective source of energy than the forms currently in use, thus scientists are striving to find a way to use hydrogen to produce it.

You must have observed while performing experiments in your labs. While performing any particular experiment if you heard Pop sounds, then we can say that there is a release of hydrogen gas. Try to perform experiments on metals with acids, high chance that they release hydrogen gas.

Today, hydrogen is gaining unheard-of momentum. The opportunity to make hydrogen a significant component of our future clean and secure energy supply should not be missed by the entire world.

Let us study its molecular form, i.e dihydrogen and a few of its important uses and properties in detail.


  • Introduction of Dihydrogen
  • Position of Hydrogen in The Periodic Table
  • Preparation of Dihydrogen
  • Physical properties of Hydrogen
  • Chemical properties of Hydrogen
  • Uses of dihydrogen
  • Practise problems
  • Frequently Asked Questions-FAQs

Introduction of Dihydrogen

The atomic structure of hydrogen is the most basic of all the elements found in nature. It only has one proton, one electron, and no neutrons in its atomic form. H has a 1s1 electrical configuration. It is known as dihydrogen when it is present as a diatomic (H2) molecule.

Position of Hydrogen in the periodic table

Helium and hydrogen are the only elements in the first period of the periodic table. Helium is inert, but hydrogen is extremely reactive. Helium's structure and properties can be easily compared to those of other noble gases in group 0 (or the 18th), but hydrogen's qualities prevent it from being related to any of the other main groups of the periodic table.

Hydrogen is the very first element in the periodic table. There is still an ongoing debate over its proposed placement due to its tendency to both gain and as well as lose an electron.

The following justifies the placement of hydrogen in group 1:

  • One electron is located in the valence shell of hydrogen, giving it an electrical configuration of 1s1.
  • It joins with other group 1 element (Li+ and Na+) to form the unipositive ion H+ (protonium ion).
  • Its valency is one.
  • Like other alkali metals, it also produces oxides, halides, and sulfides.
  • Like other alkali metals, it works effectively as a reducer in both atomic and molecule levels.

Preparation of Dihydrogen

  1. The reaction of Alkali metal with cold water:

Alkali and alkaline earth metals react with cold water to produce hydrogen. The responses are intense. Alkali metals are utilised as amalgams to reduce the rate of reaction.


  1. By applying steam to red-hot coke, hydrogen can be produced in enormous quantities and at a low cost. Water gas, a combination of CO and H2, is the end result. This is a crucial industrial fuel since it is simple to manufacture and generates a lot of heat when burned.



Since CO is challenging to extract from water gas, getting pure H2 is challenging. It is possible to separate the CO from the H2 by allowing it to liquefy under pressure at a low temperature. In a shift converter, the gas combination can also be combined with steam, cooled to 400 °C, and then passed over iron oxide to produce H2 and CO2. The CO2 thus produced is easily eliminated by either dissolving under pressure in water or by interacting with K2CO3 a solution to produce KHCO3, which then produces H2 gas.

  1. The steam reformer process also produces a significant amount of hydrogen. The hydrogen created in this manner is used to harden oils and to create NH3 in the Haber process. Steam is combined with light hydrocarbons, such as methane, and is then passed over a nickel catalyst at 800-900 °C. These hydrocarbons can be found in natural gas and are also created at oil refineries during the "cracking" process.



CO, CO2, H2 and extra steam are all present in the reformer gas that is released. More steam is added to the gas mixture, which is then cooled to 400°C before entering a shift converter. CO is transformed into CO2 by the presence of an iron/copper catalyst in this.


  1. By the action of water with metals:

(a) At room temperature (b) By heating (c) Over steam

(a) At room temperature

Metals like Na and K react with water at room temperature to give dihydrogen and metal



(b) By heating:

Heating less active metals like Zn, Mg, Al with water gives dihydrogen and metal oxide.

2Al s+ 3H2O g 2Al2O3s+ H2 g

(c) Over steam:

Metals like Fe, Ni, Co, Sn can react only when steam is passed over their red hot metals.


  1. By the reaction of metals like Zn, Al with alkalis (NaOH or KOH )

Zn, Al, Sn, Pb react with NaOH or KOH to give hydrogen gas.


2Als+2NaOHaq+ 2H2Ol2NaAlO2s+3H2g

  1. Laboratory method:

By the action of granulated zinc with dilute HCl

Hydrogen is prepared in the laboratory by the action of dilute HClon granular (commercial) zinc.Zn granulated+2HCldilZnCl2aq+H2 g

  1. Electrolysis is a method for producing dihydrogen with high purity (> 99.95 percent). By conducting a direct electric current through the aqueous or molten state of an ionic compound, electrolysis is the process of dissolving the complex into its constituent parts.

Here are the reactions taking place at the anode and cathode:

Cathode (reduction): 2H2Ol+2e-H2g+2OH-aq

Anode (oxidation): 2OH-aq12O2g+H2Ol+2e-

Main reaction can be written as:

Physical properties of Dihydrogen:

  • At room temperature, it is a colourless, flavourless, and odourless gas.
  • It cannot dissolve in water.
  • It is quite flammable.
  • The lightest gas known to us is hydrogen, which is used to fill balloons for meteorology instead of helium due to its low density.
  • The two atoms that make up hydrogen's diatomic molecule H2 are connected by a powerful covalent bond that has a bond energy of 435.9 kJ mol-1.

Chemical Properties of Dihydrogen

Under typical circumstances, hydrogen is not particularly reactive. The H—H bond strength is related to the lack of reactivity, which is caused by kinetics rather than thermodynamics. Breaking the H—H bond to create hydrogen atoms is a necessary step for H2 to react with another element. Since this requires 435.9 kJ mol-1, these processes have a high activation energy. As a result, many reactions take a long time or call for high temperatures or catalysts (often transition metals).

Heterogeneous catalysis, in which the catalyst first reacts with H2 and either breaks or weakens the H—H bond, decreases the activation energy, is a key component of many significant hydrogen processes.

Examples comprise:

  1. The Haber process, which produces NH3 from N2 and H2 at pressures of 200 atm and temperatures of 673 K.

  1. The use of Ni, Pd, or Pt catalysts that have been finely split to hydrogenate a range of unsaturated organic molecules, including the hardening of oils and vanaspati.

  1. When hydrogen burns in oxygen or dioxygen, it produces water and releases a significant quantity of energy. This is utilised while cutting and welding metals with an oxy-hydrogen flame. It is possible to reach temperatures of approximately 3000°C. Since mixes of H2 and O2 that are close to a 2:1 ratio are frequently explosive, care should be exercised when handling these gases.

2H2+O22H2O ;      ΔH=-485 kJ mol-1

  1. Halogens and hydrogen interact. Even at low temperatures, fluorine produces an aggressive reaction. The reaction with chlorine proceeds slowly in the dark but is catalysed by light (photocatalysis), speeding up in the daylight and becoming explosive in direct sunlight. To create HCl, the elements are combined directly.



Uses of Dihydrogen:

  • Vegetable oils are hydrogenated using dihydrogen.
  • Dihydrogen behaves as a reducing agent
  • used as liquid H2 rocket fuel.
  • In the production of a variety of substances, including the extensively used fertiliser urea (NH3).
  • For cutting and welding, oxy-hydrogen and atomic hydrogen torches are utilised. To produce a temperature of 4000 K on the surface to be welded, atomic hydrogen atoms (formed by the dissociation of dihydrogen with the aid of an electric arc) are permitted to recombine.
  • In the production of synthetic gasoline
  • Hydrogen-powered car engines now exist and are used now.

Practice Problems:

Q1. One commercial production of dihydrogen is

A. By the action of granulated zinc with dilute HCl
B. By the electrolysis of warm aq. Ba(OH)2 between Ni electrodes
C. By Bosch process
D. By the action of water on alkali and alkaline earth metal hydrides

Answer: C)

Solution: The Bosch process uses a sizeable amount of commercial graphite, which is then converted into hydrogen gas through the action of water (H2O).

Q2. A mixture of ________ is popularly known as syngas.

A. CO and H2O
B. H2 and CO2
C. CO and H2
D. H2O and CO2

Answer: C)

Solution: Water gas is a combination of CO and H2. This mixture is sometimes referred to as synthesis gas or syngas since it is used to create methanol and a variety of other hydrocarbons.

Q3. The catalysts used in the conversion of Acetylene to Ethane are

A. Ni,Pd,Pt
B. Hg,Na,Ni
C. Na,Zn, Mo
D. Hg,Pd,Ni

Answer: (A)

Solution: To convert Acetylene to Ethane, we generally use Ni,Pt,Pd catalysts at around 473 K.

Q4. Which gas is produced when conc. sulphuric acid combines with hydrogen gas?

A. SO3
B. H2S
C. SO2
D. O2

Answer: C)

Solution: When Conc. Sulphuric acid combines with hydrogen gas sulphur dioxide gas is released along with water. Below is the mentioned equation for this result.


Frequently asked questions-FAQ

Q 1. What is the current application of green hydrogen?
Green hydrogen is employed in a variety of industries. One of the most important is mobility, as green hydrogen is a fuel that only creates water as a by-product. Chemical, petrochemical and steel industries also use it. In addition, progress is being made in terms of its application to in-home energy and heating supplies.

Q2. Why is hydrogen seen as a sustainable fuel?
Answer: Vehicles powered by green hydrogen only release water as a byproduct, not CO2. Thus, hydrogen can be referred to as a long-term environmentally acceptable fuel.

Q3. Who came up with the name "Hydrogen"?
Answer: Antoine Lavoisier suggested the name hydrogen.(hydra means water and gennas identifies as maker which means water maker.

Q4. What is the least expensive method for making hydrogen?
Answer: To create more hydrogen, carbon monoxide and water react. The least expensive, most effective, and popular strategy is this one. In the United States, the majority of the hydrogen produced each year is created by natural gas reforming with steam.

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