Nitrogen is a fundamental chemical element, symbol N, atomic number 7. It constitutes approximately 78% of Earth’s atmosphere by volume. In its gaseous state, nitrogen is colorless, odorless, and generally non-reactive.
The Boiling Point of Nitrogen
Liquid nitrogen (LN2) has an exceptionally low boiling point, measuring approximately -196 degrees Celsius (-321 degrees Fahrenheit). The boiling point of a substance is the temperature at which its liquid form transforms into a gas. At this point, the vapor pressure of the liquid becomes equal to the surrounding atmospheric pressure.
Why Nitrogen Boils at Such a Low Temperature
The extremely low boiling point of nitrogen is directly related to the weak forces that exist between its molecules. Nitrogen exists as diatomic molecules, meaning each molecule consists of two nitrogen atoms. While the bond within each nitrogen molecule is strong, the attractive forces between separate nitrogen molecules are minimal. These intermolecular attractions are primarily weak London dispersion forces, a type of van der Waals force. Overcoming these weak forces requires very little energy. Consequently, nitrogen transitions from its liquid to its gaseous state at a significantly low temperature.
Practical Applications of Liquid Nitrogen
The low temperature of liquid nitrogen makes it valuable across many industries and scientific fields.
- In medicine and biology, it is commonly used for cryopreservation, which involves preserving biological materials such as blood, reproductive cells like sperm and eggs, and various tissues and organs for extended periods.
- Liquid nitrogen also plays a role in cryotherapy and cryosurgery, where its intense cold is applied to freeze and eliminate abnormal or unwanted tissues, including warts, skin lesions, and some precancerous growths.
- The food industry utilizes liquid nitrogen for rapid freezing processes, helping to maintain the quality, texture, color, and flavor of food products by minimizing the formation of large ice crystals.
- Beyond preservation, it is also used in culinary arts for flash-freezing ingredients and creating unique smoky effects in beverages.
- In scientific research and electronics, liquid nitrogen cools sensitive components, aids in experimental setups requiring extremely low temperatures, and helps create ultra-pure vacuum environments.
- Industrial applications include shrink-fitting metal parts, freezing pipelines for repair, and inerting or blanketing to prevent oxidation.
Safe Handling and Storage
Handling liquid nitrogen requires strict safety protocols due to its hazardous properties.
- Direct contact with liquid nitrogen or its cold vapor can cause severe frostbite, cryogenic burns, and permanent eye damage, often without immediate pain. Affected areas may appear waxy and yellow, with intense pain developing as tissue thaws.
- Liquid nitrogen expands dramatically, with one liter of liquid converting into approximately 700 liters of gas when it vaporizes.
- This expansion can displace oxygen in poorly ventilated or confined spaces, leading to oxygen deficiency below safe levels, which may cause dizziness, nausea, unconsciousness, or even death without warning.
- Storing liquid nitrogen in sealed containers is dangerous, as pressure build-up from vaporization can cause explosions; containers must always be equipped with pressure-relief devices.
- When working with liquid nitrogen, appropriate personal protective equipment is essential, including loose-fitting thermal insulated or leather gloves, a full face shield worn over safety glasses or goggles, long-sleeved shirts, trousers without cuffs, and closed-toe shoes.
- It should only be used and stored in well-ventilated areas and handled by trained professionals.