The chemical formula is N2, which is usually a colorless and odorless gas, and nitrogen is generally less dense than air. Nitrogen accounts for 78.08% (volume fraction) of the total atmosphere and is the main component of air. Under standard atmospheric pressure, when cooled to -195.8°C, it becomes a colorless liquid, and when cooled to -209.8°C, liquid nitrogen becomes a snow-like solid. Nitrogen is chemically inactive and difficult to react with other substances at room temperature, so it is often used to make preservatives. However, it can undergo chemical changes with certain substances under high temperature and high energy conditions to produce new substances useful to humans.

Basic Information

Chemical nature

It can also be seen from the oxidation state-Gibbs free energy diagram of nitrogen that, in addition to NH4 ions, the N2 molecule with an oxidation number of 0 is at the lowest point of the curve in the figure, which shows that it is relative to other nitrogen compounds with an oxidation number. In terms of speaking, N2 is a thermodynamically stable state structure. The values of various nitrogen compounds with oxidation numbers between 0 and +5 are all located above the line connecting the two points of HNO3 and N2 (the dotted line in the figure). Therefore, these compounds are thermodynamically unstable and prone to disproportionation reactions. The only one with lower molecular value than N2 in the figure is NH4 ion.

Positive nitrogen is acidic, and negative nitrogen is basic.

The triple bond energy in the nitrogen molecule is very large and it is not easy to be destroyed, so its chemical properties are very stable. Only under the conditions of high temperature and pressure and the presence of a catalyst, nitrogen can react with hydrogen to form ammonia. At the same time, because the chemical structure of the nitrogen molecule N2 is relatively stable, the structure of C2 and nitrogen in the cyanide ion CN and calcium carbide CaC2 are similar.

Physical properties

Nitrogen is a colorless and odorless gas under normal conditions. It has a melting point of 63 K, a boiling point of 77 K, and a critical temperature of 126 K. It is difficult to liquefy. The solubility is very small. One volume of water can dissolve 0.02 volume of nitrogen at 283 K under normal pressure.

Nitrogen is a gas that is difficult to liquefy. Nitrogen will liquefy into a colorless liquid at extremely low temperatures. When the temperature is further reduced, a white crystalline solid will be formed. In production, black steel cylinders are usually used to hold nitrogen. See the table below for other physical properties:

Nitrogen use

Chemical synthesis

The main way for humans to effectively use nitrogen is to synthesize ammonia, but the requirements are very high. In recent years, people have tried their best to understand the mechanism of nitrogen fixation in plants, and strive to simulate biological nitrogen fixation with chemical methods to realize the development and utilization of nitrogen resources in the air under mild conditions. Nitrogen is mainly used to synthesize ammonia. The reaction formula is nitrogen introduction (conditions are high pressure, high temperature, and catalyst. The reaction is a reversible reaction). It is also an important raw material for synthetic fibers (nylon, acrylic), synthetic resin, and synthetic rubber. Nitrogen is a nutrient element and can also be used to make fertilizers. For example: ammonium bicarbonate NH4HCO3, ammonium chloride NH4Cl, ammonium nitrate NH4NO3 and so on.

Other uses

Due to the chemical inertness of nitrogen, it is often used as a protective gas, such as: melons, fruits, food, bulb filling gas. In order to prevent certain objects from being oxidized by oxygen when exposed to the air, filling the granary with nitrogen can prevent the grain from rotten, sprouting and long-term storage. Liquid nitrogen can also be used as a deep refrigerant. It is often used as a refrigerant in hospitals for removing spots, bags, beans, etc., that is, freezing off spots, bags, beans, etc., but it is prone to scars, so it is not recommended. High-purity nitrogen is used as a carrier gas for chromatographs and other instruments. Used as a protective gas for bright annealing of copper tubes. Together with high-purity helium and high-purity carbon dioxide, it is used as the laser gas for laser cutting machines. Nitrogen is also used as a protective gas for food preservation. In the chemical industry, nitrogen is mainly used as protective gas, replacement gas, scrubbing gas, and safety gas. Used as a protective gas for aluminum products, aluminum profile processing, and aluminum thin rolling. Used as a shielding gas for reflow soldering and wave soldering to improve soldering quality. Used as a protective gas in the production of float glass to prevent oxidation in the tin bath. 

Precautions

risk

Hazard category: Class 2.2 inert gas

Invasion route: inhalation

Health hazards: Too high nitrogen content in the air reduces the partial pressure of inhaled oxygen, causing hypoxia asphyxiation. When the inhaled nitrogen concentration is not too high, the patient initially feels chest tightness, shortness of breath, weakness, and then irritability, extreme excitement, running around, yelling, trance, and unsteady gait. This is called "nitrogen tincture" and may enter lethargy. Or coma. Inhalation of high concentrations, patients can quickly become unconscious and die due to the arrest of breathing and heartbeat.

When divers dive deep, the anesthesia effect of nitrogen can occur; if you switch from a high-pressure environment to a normal pressure environment too quickly, nitrogen bubbles will form in the body, compressing nerves and blood vessels or causing capillaries to block, resulting in "decompression sickness".

Environmental hazards: none

Explosion hazard: This product is non-flammable.

first-aid

Skin contact: Nothing (because the air contains about 78% nitrogen)

Eye contact: It's okay (the reason is the same as above)

Inhalation: (when the concentration is high) quickly leave the scene to a place with fresh air. Keep the airway open. If breathing is difficult, give oxygen. When breathing and heartbeat stop, perform artificial respiration and chest compressions immediately. Seek medical attention.

Fire-fighting measures

Hazard characteristics: In case of high heat, the internal pressure of the container will increase, and there will be a risk of cracking and explosion.

Hazardous combustion products: nitrogen.

Extinguishing method: This product is non-flammable. Move the container from the fire scene to an open place as much as possible. Spray water to keep the fire container cool, and keep the container in the fire scene cool with mist water until the end of the fire. Water spray can be used to accelerate the evaporation of liquid nitrogen, but the water gun can not be used to shoot the liquid nitrogen.

Leakage emergency treatment

Emergency treatment: quickly evacuate personnel from the leaked contaminated area to the upper wind, and isolate them, strictly restrict access. It is recommended that emergency response personnel wear self-contained positive pressure breathing apparatus and general work clothes. Cut off the source of leakage as much as possible. Reasonable ventilation to accelerate diffusion. Leaking containers should be properly handled and used after repair and inspection.