Density of nitrogen

Nitrogen is a chemical element of the periodic system, designated by the letter N and having the serial number 7. It exists in the form of a molecule N2, consisting of two atoms. This chemical is a colorless, odorless and without taste gas, it is inert under standard conditions. The density of nitrogen under normal conditions (at 0 ° C and pressure 101.3 kPa) is 1.251 g / dm3. The element is part of the Earth's atmosphere in an amount of 78.09% of its volume. It was first discovered as a component of air by the Scottish physician Daniel Rutherford in 1772.

Liquid nitrogen is a cryogenic liquid. At atmospheric pressure, it boils at a temperature of -195.8 ° C. Therefore, it can be stored only in isolated vessels, which are steel cylinders for liquefied gases or Dewar vessels. Only in this case it can be stored or transported without special losses due to evaporation. Like dry ice (liquefied carbon dioxide, otherwise called carbon dioxide), liquid nitrogen is used as a coolant. In addition, it is used for cryopreservation of blood, sex cells (spermatozoa and eggs), as well as other biological samples and materials. It is in demand in clinical practice, for example, in cryotherapy when removing cysts and warts on the skin. The density of liquid nitrogen is 0.808 g / cm3.

Many industrially important compounds, such as nitric acid, ammonia, organic nitrates (explosives, fuel) and cyanides, contain N2. Extremely strong bonds of elemental nitrogen in the molecule cause difficulties for its participation in chemical reactions, which explains its inertness under standard conditions (temperature and pressure). Including for these reasons N2 is of great importance in many scientific and industrial fields. For example, it is necessary to maintain in-situ pressure when extracting oil or gas. Any of its practical or scientific applications require knowing what the density of nitrogen will be at a particular pressure and temperature. It is known from the laws of physics and thermodynamics that for a constant volume, with increasing temperature, the pressure and density of the gas will increase , and vice versa.

When and why do you need to know the density of nitrogen? Calculation of this indicator is used in the design of technological processes that take place using N2, in laboratory practice and in production. Using a known value of the gas density, it is possible to calculate its mass in a certain volume. For example, it is known that the gas occupies a volume of 20 dm3 under normal conditions. In this case, its mass can be calculated: m = 20 • 1,251 = 25.02 g. If the conditions are different from the standard ones, and the volume of N2 is known under these conditions, it is first necessary to find (according to the directories) the density of nitrogen at a certain pressure and temperature, and Then multiply this by the volume occupied by the gas.

Similar calculations are carried out in production during the compilation of material balances of technological installations. They are necessary for the conduct of technological processes, selection of instrumentation, calculation of technical and economic indicators, and so on. For example, after stopping chemical production, all apparatuses and pipelines must be purged with an inert gas, nitrogen before it is opened and put out for repair (it is the cheapest and most affordable in comparison, for example, with helium or argon). As a rule, they are blown with such an amount of N2, which is several times larger than the volume of apparatus or piping, only this way it is possible to remove flammable gases and vapors from the system and to exclude an explosion or fire. When planning operations before stopping repair, the technologist, knowing the volume of the emptying system and the density of nitrogen, calculates the mass of N2 that will be required for purging.

For simplified calculations that do not require accuracy, real gases are equated to ideal gases and Avogadro's law is applied. Since the mass of 1 mole of N2 is numerically equal to 28 grams, and 1 mole of any ideal gas occupies a volume of 22.4 liters, the nitrogen density will be equal to: 28 / 22.4 = 1.25 g / l = 1.25 g / dm3. This method of rapid determination of the density is applicable for any gas, and not only for N2. It is often used in analytical laboratories.