The question of whether nitrogen is an inert gas requires a careful distinction between the strict chemical definition and how the gas behaves in practice. Nitrogen gas (N2) is the most abundant component of Earth’s atmosphere, constituting about 78% of the air we breathe. While it is widely used in industrial and commercial applications specifically for its non-reactive properties, nitrogen is not classified as a chemically inert gas. The answer is nuanced, rooted in the difference between a molecule’s inherent stability and the energy required to make it react.
What Defines an Inert Gas
The strict chemical classification of an inert gas belongs exclusively to the Noble Gases (Group 18 of the periodic table), including helium, neon, argon, krypton, and xenon. These gases possess a full valence electron shell, meaning their outermost orbitals are completely occupied with electrons. Because they have no tendency to gain, lose, or share electrons, Noble Gases exhibit near-zero reactivity under standard atmospheric conditions. This intrinsic lack of desire to form chemical bonds is the definition of true chemical inertness.
Nitrogen’s Unique Stability
Nitrogen’s apparent inertness stems not from a completed electron shell but from the extraordinary strength of its chemical bond. The two nitrogen atoms in the N2 molecule are joined by a triple covalent bond, where three pairs of electrons are shared between them. This specific arrangement is one of the strongest bonds found in any diatomic molecule, requiring a substantial 945 kilojoules per mole of energy to break. The high energy needed to initiate a reaction creates a significant kinetic barrier, known as the activation energy.
Thermodynamically, nitrogen has the potential to react with many substances, but the reaction rate is exceptionally slow at room temperature and pressure. The triple bond holds the atoms together so tightly that ordinary thermal energy is insufficient to break it and allow new compounds to form. This effect, where a substance is stable because of the high energy required to start the reaction, is referred to as kinetic stability. Nitrogen is therefore best described as kinetically stable rather than truly chemically inert.
When Nitrogen is Not Inert
The kinetic stability of nitrogen can be overcome by supplying a large amount of energy, proving that it is not fundamentally inert. In nature, this happens through biological nitrogen fixation, a process performed by certain bacteria and archaea. These microorganisms use a complex enzyme called nitrogenase, which, powered by the hydrolysis of adenosine triphosphate (ATP), manages to break the triple bond and convert atmospheric nitrogen into ammonia (NH3). This biological pathway is absolutely necessary for life on Earth, as it makes nitrogen available for the synthesis of proteins and nucleic acids.
On an industrial scale, the triple bond is broken in the highly energy-intensive Haber-Bosch process, which synthesizes ammonia for fertilizer production. This industrial method requires extreme conditions, specifically high temperatures ranging from 400 to 500 °C and high pressures between 150 to 250 atmospheres. A specialized catalyst, typically iron-based, is used to lower the activation energy, but the process still consumes a significant percentage of the world’s annual energy supply.
Real-World Uses of Nitrogen’s Low Reactivity
Nitrogen’s kinetic stability and resistance to reaction under normal conditions make it highly valuable in industry. It is commonly utilized as an “inert blanketing agent” or purging gas to displace atmospheric oxygen. This application is crucial in preventing unwanted oxidation reactions that can degrade sensitive materials.
For instance, in the food industry, nitrogen gas is used to flush out oxygen from bags of chips and other packaged goods, which extends shelf life and prevents the fats from becoming rancid. In chemical storage and transport, nitrogen blanketing fills the empty space above flammable liquids in storage tanks. This displaces oxygen, removing one element of the fire triangle and significantly reducing explosion risk. High-purity nitrogen is also employed in the manufacturing of electronics and pharmaceuticals to protect sensitive components and products from moisture and oxidation during processing.