Is Hydrogen Reactive? (Why Yes? & Why No?)

The reactivity of hydrogen depends on its state. Molecular hydrogen (H2) is relatively unreactive at room temperature, ¹ but it can be made to react with other elements by increasing the temperature or by using a catalyst. Atomic hydrogen, on the other hand, is highly reactive and can combine with most elements to form hydrides. ²

Well, this was just a simple answer. But there are few more things to know about this topic which will make your concept super clear.

So let’s dive right into it.

Nonreactive state of hydrogen

Molecular hydrogen (H₂) is a colorless, odorless, and tasteless gas that is the simplest and most abundant element in the universe. Molecular hydrogen is relatively unreactive at room temperature. ^{3 4}

This is because the H-H bond in molecular hydrogen is very strong, with a bond dissociation energy of 436 kJ/mol. ⁵

This means that it requires a lot of energy to break the H-H bond and form new chemical bonds.

Examples

There are a few examples of how the low reactivity of molecular hydrogen can be observed. 

For example, molecular hydrogen will not react with oxygen at room temperature, even though oxygen is a very reactive element. ⁶

Similarly, molecular hydrogen will not react with chlorine or fluorine at room temperature. 

However, if the temperature is raised or if a catalyst is present, molecular hydrogen can react with these elements.

The low reactivity of molecular hydrogen can be a disadvantage in some cases. For example, it makes it difficult to store and transport molecular hydrogen. ⁷

However, the low reactivity of molecular hydrogen can also be an advantage. For example, it makes molecular hydrogen a safe and clean fuel. ⁸

Reactive state of hydrogen

Atomic hydrogen is a single hydrogen atom, while molecular hydrogen is a pair of hydrogen atoms bonded together. Atomic hydrogen is more reactive than molecular hydrogen because it has more energy. ⁹

This is because the electrons in an atomic hydrogen atom are not shared with another atom, so they have more energy. 

When atomic hydrogen reacts with another atom, the electrons in the atomic hydrogen atom are shared with the other atom. This releases energy, which makes the reaction exothermic (releases heat). ¹⁰

Examples

Here are some examples of reactions that involve atomic hydrogen:

• Hydrogen + oxygen —> water
• Hydrogen + chlorine —> hydrogen chloride
• Hydrogen + carbon —> methane
• Hydrogen + metal —> metal hydride

In all of these reactions, the atomic hydrogen atom reacts with another atom to form a new compound. The reaction releases energy, which makes it exothermic.

The reactivity of atomic hydrogen can be used to create useful products, such as water and fuels. ¹¹

However, it can also be dangerous, as it can be explosive when mixed with oxygen. ¹²

Further reading

Why is Hydrogen Diatomic?
Is Hydrogen a Compound?
Is Hydrogen a Metal? 
Are Alkaline Earth Metals Reactive?
Why are Noble Gases Unreactive?

1. The Chemistry of Hydrogen. (n.d.). The Chemistry of Hydrogen. https://chemed.chem.purdue.edu/genchem/topicreview/bp/ch10/hydrogen.php
2. 2.4: Atomic Hydrogen. (2020, April 17). Chemistry LibreTexts. https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Chemistry_of_the_Main_Group_Elements_(Barron)/02%3A_Hydrogen/2.04%3A_Atomic_Hydrogen
3. US GOV, N. O. (n.d.). HYDROGEN | CAMEO Chemicals | NOAA. HYDROGEN | CAMEO Chemicals | NOAA. https://cameochemicals.noaa.gov/chemical/8729
4. Hydrogen explained – U.S. Energy Information Administration (EIA). (2023, May 4). Hydrogen Explained – U.S. Energy Information Administration (EIA). https://www.eia.gov/energyexplained/hydrogen/
5. Chemistry, life, the universe and everything. (n.d.). Chemistry, Life, the Universe and Everything. https://virtuallaboratory.colorado.edu/CLUE-Chemistry/chapters/chapter7txt-6.html
6. Hydrogen – Wikipedia. (2021, December 25). Hydrogen – Wikipedia. https://en.wikipedia.org/wiki/Hydrogen
7. Hydrogen – Reactivity of hydrogen. (n.d.). Encyclopedia Britannica. https://www.britannica.com/science/hydrogen
8. Hydrogen Fuel Basics. (n.d.). Energy.gov. https://www.energy.gov/eere/fuelcells/hydrogen-fuel-basics
9. Hydrogen – Reactivity of hydrogen. (n.d.). Encyclopedia Britannica. https://www.britannica.com/science/hydrogen
10. Yale.edu http://ursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/thermo/thermointro.html
11. Scientists discover new way to make water | Chemistry at Illinois. (n.d.). Scientists Discover New Way to Make Water | Chemistry at Illinois. https://chemistry.illinois.edu/news/2007-12-31/scientists-discover-new-way-make-water
12. Kujan, S. L. (n.d.). Explosive Reaction of Hydrogen and Oxygen Using Balloons. Explosive Reaction of Hydrogen and Oxygen Using Balloons. https://rutchem.rutgers.edu/cldf-demos/1028-cldf-demo-balloons