The chemical element nitrogen has the symbol N, atomic number 7 and atomic mass 14. In the elemental state, nitrogen forms very stable diatomic molecules N 2 with strong interatomic bonds.
Nitrogen molecule, its size and gas properties
The nitrogen molecule is formed by a triple covalent bond between two nitrogen atoms and has the chemical formula N2. The size of the molecules of most substances in general, and nitrogen in particular, is a rather difficult value to determine, and even the concept itself is not unambiguous. To understand the operating principles of equipment that separates air components, the best concept is kinetic diameter molecule, which is defined as the smallest dimension of a molecule. Nitrogen N 2, as well as oxygen O 2, are diatomic molecules, more similar in shape to cylinders than to spheres - therefore, one of their dimensions, which can conventionally be called “length,” is more significant than the other, which is conventionally can be called "diameter". Even the kinetic diameter of a nitrogen molecule is not unambiguously determined, however, there is data obtained both theoretically and experimentally on the kinetic diameter of nitrogen and oxygen molecules (we present data on oxygen because oxygen is the second main component of atmospheric air, and it is from it it is necessary to purify nitrogen when it is obtained during the air separation process), including:
- N 2 3.16Å and O 2 2.96Å - from viscosity data
- N 2 3.14Å and O 2 2.90Å - from data on van der Waals forces
Nitrogen N 2 melts, that is, passes from the solid phase to the liquid, at a temperature of -210°C, and evaporates (boils), that is, passes from a liquid to a gaseous state, at a temperature of -195.79°C.
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Nitrogen gas is an inert gas, colorless, tasteless, odorless, non-flammable and non-toxic. The density of nitrogen under normal atmospheric conditions (that is, at a temperature of 0°C and an absolute pressure of 101325 Pa) is 1.251 kg/m³. Nitrogen does not react with virtually any other substances (with the exception of rare reactions of nitrogen binding with lithium and magnesium). Also, on the contrary, the Haber process is widely used in industry, in the production of fertilizers, in which, in the presence of a catalyst, iron trioxide Fe 3 O 4, nitrogen is bonded with hydrogen at high temperature and pressure.
Nitrogen makes up the bulk of the earth's atmosphere, both by volume (78.3%) and mass (75.47%). Nitrogen is present in all living organisms, in dead organisms, in waste products of organisms, in protein molecules, nucleic acids and amino acids, urea, uric acid and other organic molecules. In nature, there are also nitrogen-containing minerals: nitrate (potassium nitrate - potassium nitrate KNO 3, ammonium nitrate - ammonium nitrate NH 4 NO 3, sodium nitrate - sodium nitrate NaNO 3, magnesium nitrate, barium nitrate, etc.), ammonia compounds (for example, ammonium chloride NH 4 Cl, etc.) and other, mostly quite rare, minerals.
Publication date 02/16/2013 03:40
Nitrogen– a chemical element of the periodic table, denoted by the letter N and having an atomic number 7. It exists in the form of a molecule N2, consisting of two atoms. This chemical is a colorless, odorless, and tasteless gas that 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 the amount of 78.09% of its volume. It was first discovered as a component of air by 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 only be stored in insulated containers, which are steel cylinders for liquefied gases or Dewar flasks. Only in this case can it be stored or transported without much loss due to evaporation. Like dry ice (liquefied carbon dioxide, otherwise known as carbon dioxide), liquid nitrogen is used as a refrigerant. In addition, it is used for cryopreservation of blood, germ cells (sperm and eggs), as well as other biological samples and materials. It is also in demand in clinical practice, for example, in cryotherapy for the removal of 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, fuels) and cyanides, contain N2. The extremely strong bonds of elemental nitrogen in the molecule make it difficult for it to participate in chemical reactions, this explains its inertness under standard conditions (temperature and pressure). Also for these reasons, N2 is of great importance in many scientific and industrial fields. For example, it is necessary to maintain in-situ pressure during oil or gas production. Any practical or scientific application of it requires 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 at a constant volume, the pressure and density of the gas will increase with increasing temperature, and vice versa.
When and why you need to know nitrogen density? The calculation of this indicator is used in the design of technological processes using N2, in laboratory practice and in production. Using the known density of a gas, its mass in a certain volume can be calculated. For example, it is known that gas occupies a volume of 20 dm3 under normal conditions. In this case, you can calculate its mass: m = 20 1.251 = 25.02 g. If conditions are different from standard, and the volume of N2 under these conditions is known, then you will need to first find (from reference books) the density of nitrogen at a certain pressure and temperature, and then multiply this value by the volume occupied by the gas.
Similar calculations are carried out in production when compiling material balances of technological installations. They are necessary for conducting technological processes, selecting instrumentation, calculating technical and economic indicators, etc. For example, after stopping chemical production, all devices and pipelines must be purged with an inert gas - nitrogen (it is the cheapest and most accessible compared, for example, with helium or argon) before opening them and taking them out for repairs. As a rule, they are purged with an amount of N2 that is several times greater than the volume of the apparatus or pipelines; this is the only way to remove flammable gases and vapors from the system and prevent an explosion or fire. When planning operations before shutdown repairs, the technologist, knowing the volume of the system to be emptied and the density of nitrogen, calculates the mass of N2 that will be required for purging.
Nitrogen is a chemical element of the periodic table, denoted 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 tasteless gas that 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 included in the composition in an amount of 78.09% of its volume. It was first discovered as a component of air by Scottish physician Daniel Rutherford in 1772.
Liquid nitrogen is a cryogenic liquid. At atmospheric pressure it boils at - 195.8 °C. Therefore, it can only be stored in insulated containers, which are steel cylinders for liquefied gases or Only in this case can it be stored or transported without significant losses due to evaporation. Like dry ice (liquefied, otherwise known as carbon dioxide), liquid nitrogen is used as a refrigerant. In addition, it is used for cryopreservation of blood, germ cells (sperm and eggs), as well as other biological samples and materials. It is also in demand in clinical practice, for example, in cryotherapy for the removal of cysts and warts on the skin. The density of liquid nitrogen is 0.808 g/cm3.
Many industrially important compounds, such as ammonia, organic nitrates (explosives, fuels) and cyanides, contain N2. The extremely strong bonds of elemental nitrogen in the molecule make it difficult for it to participate in chemical reactions, which explains its inertness under standard conditions (temperature and pressure). Also for these reasons, N2 is of great importance in many scientific and industrial fields. For example, it is necessary to maintain in-situ pressure during oil or gas production. Any practical or scientific application of it requires 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 at a constant volume, pressure will increase with increasing temperature and vice versa.
When and why do you need to know the density of nitrogen? The calculation of this indicator is used in the design of technological processes using N2, in laboratory practice and in production. Using the known density of a gas, its mass in a certain volume can be calculated. For example, it is known that gas occupies a volume of 20 dm3 under normal conditions. In this case, you can calculate its mass: m = 20. 1.251 = 25.02 g. If the conditions are different from standard ones, and the volume of N2 under these conditions is known, then you will need to first find (using reference books) the density of nitrogen at a certain pressure and temperature, and then multiply this value by the volume occupied by the gas.
Similar calculations are carried out in production when compiling material balances of technological installations. They are necessary for conducting technological processes, selecting instrumentation, calculating technical and economic indicators, etc. For example, after stopping chemical production, all devices and pipelines must be purged with an inert gas - nitrogen (it is the cheapest and most accessible compared to, for example, helium or argon) before opening them and taking them out for repairs. As a rule, they are purged with an amount of N2 that is several times greater than the volume of the apparatus or pipelines; this is the only way to remove flammable gases and vapors from the system and prevent an explosion or fire. When planning operations before shutdown repairs, the technologist, knowing the volume of the system to be emptied 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 density of nitrogen will be equal to: 28/22.4 = 1.25 g/l = 1.25 g/dm3. This method of quickly finding density is applicable to any gas, not just N2. It is often used in analytical laboratories.
The table shows the density of nitrogen and its thermophysical properties in the gaseous state depending on temperature and pressure. The thermophysical properties of nitrogen are given at temperatures from 0 to 1000°C and pressure from 1 to 100 atmospheres.
As can be seen from the table, such properties of nitrogen as thermal diffusivity and kinematic viscosity strongly depend on temperature. With increasing pressure, these properties of nitrogen decrease their values, while nitrogen density increases significantly. For example, at atmospheric pressure and a temperature of 0°C, the density of nitrogen is 1.21 kg/m3, and with an increase in pressure 100 times, the density of nitrogen increases to 122.8 kg/m3 at the same temperature.
The specific heat capacity of nitrogen increases with increasing temperature of this gas. As pressure increases, the specific heat capacity of nitrogen also increases. For example, at a temperature of 0°C and atmospheric pressure The specific heat capacity of nitrogen is 1039 J/(kg deg), and when this gas is compressed to a pressure of 100 atmospheres, it will be 1242 J/(kg deg) at the same temperature.
It should be noted that at high temperatures (about 1000°C) the influence of pressure on the specific heat capacity of nitrogen decreases. So, at a temperature of 1000°C and a pressure of 1 and 100 atm. the heat capacity value will be equal to 1215 and 1219 J/(kg deg) respectively.
The table shows the following properties of nitrogen:
- nitrogen density γ , kg/m 3 ;
- specific heat C p , kJ/(kg deg);
- thermal conductivity coefficient λ , W/(m deg);
- dynamic viscosity μ , ;
- thermal diffusivity a , m 2 /s;
- kinematic viscosity ν , m 2 /s;
- Prandtl number Pr .
Density of dissociated nitrogen at high temperatures.
The table gives the density values of nitrogen in the dissociated and ionized state at pressures from 0.2 to 100 atmospheres at high temperatures. The density of nitrogen in the gaseous state is given in the temperature range 5000...40000 K in the dimension kg/m 3.
The density of nitrogen decreases with increasing temperature and increases with increasing gas pressure. The value of the specific gravity of nitrogen (its density) in the table ranges from 0.00043 to 6.83 kg/m3. For example, at atmospheric pressure and a temperature of 5000 K (4727 ° C), the density of nitrogen is 0.0682 kg/m 3. When nitrogen is heated to a temperature of 40,000 K, its density decreases to a value of 0.00213 kg/m 3.
Note: Be careful! The density of nitrogen in the table is indicated in powers of 10 3. Don't forget to divide by 1000.
Thermal conductivity of nitrogen in liquid and gaseous states
The table shows the thermal conductivity of nitrogen in liquid and gaseous states depending on temperature and pressure.
The thermal conductivity of nitrogen (dimension W/(m deg)) is indicated in the temperature range from -193 to 1127 °C and pressure from 1 to 600 atmospheres.
Thermal conductivity of dissociated nitrogen at high temperatures.
The table gives the thermal conductivity values of dissociated nitrogen at pressures from 0.001 to 100 atmospheres and high temperatures.
The thermal conductivity of nitrogen in the gaseous state is given in the temperature range 2000...6000 K in the dimension W/(m deg).
The value of the thermal conductivity coefficient of nitrogen increases with increasing temperature and generally decreases with increasing pressure of this gas. The thermal conductivity of dissociated nitrogen under the conditions considered in the table varies from 0.126 to 6.142 W/(m deg).
Be careful! The thermal conductivity of nitrogen in the table is indicated to the power of 10 3. Don't forget to divide the table value by 1000.
Thermal conductivity of liquid nitrogen at the saturation line.
The table shows the values of the thermal conductivity coefficient of liquid nitrogen on the saturation line at low temperatures.
The thermal conductivity of liquid nitrogen is indicated at temperatures of 90...120 K (-183...-153°C).
The table shows that the thermal conductivity of nitrogen in the liquid state decreases with increasing temperature.
Note: Be careful! The thermal conductivity of nitrogen in the table is indicated to the power of 10 3. Don't forget to divide by 1000.
Dynamic viscosity of nitrogen depending on temperature and pressure
The table shows nitrogen values depending on temperature and pressure.
The dynamic viscosity of nitrogen (dimension Pa s) is indicated in the temperature range from 80 to 6000 K and pressure from 1 to 400 atmospheres and from 0.001 to 100 atmospheres.
At a nitrogen temperature of 3600 K, it begins to partially dissociate. As the temperature of azoate gas increases, its dynamic viscosity increases. As the temperature of liquid nitrogen increases, the value of its dynamic viscosity also increases.
Note: Be careful! The viscosity of nitrogen in the table is indicated in powers of 10 6. Don't forget to divide by 10 6 .
Sources:
- Physical quantities. Directory. A.P. Babichev, N.A. Babushkina, A.M. Bratkovsky and others; Ed. I.S. Grigorieva, E.Z. Meilikhova. - M.: Energoatomizdat, 1991. - 1232 p.
DEFINITION
Nitrogen- non-metal. Under normal conditions, it is a colorless gas that can condense into a colorless liquid(density of liquid nitrogen is 0.808 g/cm 3), boiling, unlike liquid oxygen, at a lower temperature (-195.75 o C) than liquid oxygen.
In the solid state it appears as white crystals.
Nitrogen is poorly soluble in water (worse than oxygen), but it is highly soluble in liquid sulfur dioxide.
Chemical composition and structure of the liquid nitrogen molecule
Under normal conditions, nitrogen is a colorless gas consisting of N 2 molecules. There is a triple bond between the nitrogen atoms in the molecule, as a result of which its molecule is extremely strong. Molecular nitrogen is chemically inactive and weakly polarized.
Let us consider the formation of a nitrogen molecule (Fig. 1), the electron cloud of which has the shape of an elongated figure eight. When two nitrogen atoms approach, their electron clouds overlap. Such overlap is possible only when the electrons have antiparallel spins. In the region of cloud overlap, the electron density increases, as a result of which the attractive forces between atoms increase. The number of shared electron pairs in a nitrogen molecule is equal to one (one electron from each atom). The molecule has a covalent (non-polar) type of bond.
Rice. 1. The structure of the nitrogen molecule.
Brief description of the chemical properties and density of liquid nitrogen
Under normal conditions, nitrogen is a chemically passive element; does not react with acids, alkalis, ammonia hydrate, halogens, sulfur. Reacts to a small extent with hydrogen and oxygen under the action of an electric discharge (1, 2). In the presence of moisture, it reacts with lithium at room temperature (3). When heated, it reacts with magnesium, calcium, aluminum and other metals (4, 5, 6).
N 2 + 3H 2 ↔ 2NH 3 (1);
N 2 + O 2 ↔ 2NO (2);
N 2 + 6Li = 2Li 3 N (3);
N 2 + 3Mg = Mg 3 N_2 (4);
N 2 + 3Ca = Ca 3 N 2 (5);
N 2 + 2Al = 2AlN (6).
The reactions of nitrogen with fluorine and carbon, as in the case of hydrogen or oxygen, occur under the action of an electric discharge:
N 2 + 3F 2 = 2NF 3 ;
N 2 + 2C↔C 2 N 2.
When heated to a temperature of 500-600 o C, nitrogen reacts with lithium hydride (7), but if the temperature range is 300-350 o C, then a reaction with calcium carbide (8) is possible:
N 2 + 3LiH = Li 3 N + NH 3 (7);
N 2 + CaC 2 = Ca(CN) 2 (8).
Examples of problem solving
EXAMPLE 1
| Exercise | The gas density in air is 2.564. Calculate the mass of gas with a volume of 1 liter (n.s.). |
| Solution | The ratio of the mass of a given gas to the mass of another gas taken in the same volume, at the same temperature and the same pressure is called the relative density of the first gas to the second. This value shows how many times the first gas is heavier or lighter than the second gas. The molar mass of a gas is equal to its density relative to another gas, multiplied by the molar mass of the second gas: The relative molecular weight of air is taken to be 29 (taking into account the content of nitrogen, oxygen and other gases in the air). It should be noted that the concept of “relative molecular mass of air” is used conditionally, since air is a mixture of gases. Then, the molar mass of the gas will be equal to: M gas = D air × M(air) = 2.564 × 29 = 74.356 g/mol. m(gas) = n(gas) ×M gas . Let's find the amount of gas substance: V(gas) = n(gas) ×V m ; n(gas) = V(gas) / V m = 1 / 22.4 = 0.04 mol. m(gas) = 0.04 × 74.356 = 2.97 g. |
| Answer | The mass of the gas is 2.97 g. |
