DEFINITION

atmospheric air is a mixture of many gases. Air has a complex composition. Its main components can be divided into three groups: constant, variable and random. The former include oxygen (the oxygen content in the air is about 21% by volume), nitrogen (about 86%) and the so-called inert gases (about 1%).

Content constituent parts virtually independent of where the globe a sample of dry air was taken. The second group includes carbon dioxide (0.02 - 0.04%) and water vapor (up to 3%). The content of random constituents depends on local conditions: near metallurgical plants, appreciable amounts are often mixed into the air. sour gas, in places where the decay of organic residues occurs - ammonia, etc. In addition to various gases, air always contains more or less dust.

Air density is a value equal to the mass of gas in the Earth's atmosphere divided by a unit volume. It depends on pressure, temperature and humidity. There is a standard air density value - 1.225 kg / m 3, corresponding to the density of dry air at a temperature of 15 o C and a pressure of 101330 Pa.

Knowing from experience the mass of a liter of air under normal conditions (1.293 g), one can calculate the molecular weight that air would have if it were an individual gas. Since a gram-molecule of any gas under normal conditions occupies a volume of 22.4 liters, the average molecular weight of air is

22.4 × 1.293 = 29.

This number - 29 - should be remembered: knowing it, it is easy to calculate the density of any gas in relation to air.

Density of liquid air

When cool enough, the air moves into liquid state. Liquid air can be stored for quite a long time in vessels with double walls, from the space between which air is pumped out to reduce heat transfer. Similar vessels are used, for example, in thermoses.

Freely evaporating under normal conditions, liquid air has a temperature of about (-190 o C). Its composition is unstable, since nitrogen evaporates easier than oxygen. As nitrogen is removed, the color of liquid air changes from bluish to pale blue (the color of liquid oxygen).

In liquid air, ethyl alcohol, diethyl ether and many gases easily turn into a solid state. If, for example, carbon dioxide is passed through liquid air, then it turns into white flakes, similar in appearance to the snow. Mercury immersed in liquid air becomes solid and malleable.

Many substances cooled by liquid air change their properties dramatically. Thus, chink and tin become so brittle that they easily turn into powder, a lead bell makes a clear ringing sound, and a frozen rubber ball shatters if dropped on the floor.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

Exercise	Determine how many times heavier than air hydrogen sulfide H 2 S.
Decision	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 over the second. This value shows how many times the first gas is heavier or lighter than the second gas. The relative molecular weight of air is taken equal to 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 weight of air" is used conditionally, since air is a mixture of gases. D air (H 2 S) = M r (H 2 S) / M r (air); D air (H 2 S) = 34/29 = 1.17. M r (H 2 S) = 2 × A r (H) + A r (S) = 2 × 1 + 32 = 2 + 32 = 34.
Answer	Hydrogen sulfide H 2 S is 1.17 times heavier than air.

Natural gas is a mixture of hydrocarbon gases, occurring in the subsoil in the form of separate deposits and deposits, as well as in dissolved form in oil deposits or in the form of so-called "gas caps". Basic physical and Chemical properties natural gas This:

The density of gases is the mass of a substance per unit volume - g / cm 3. For practical purposes, the relative density of the gas relative to air is used, i.e. ratio of gas density to air density. In other words, it is an indicator of how much a gas is lighter or heavier than air:

where ρ in under standard conditions is 1.293 kg / m 3;

The relative density of methane is 0.554, ethane is 1.05, and propane is 1.55. That is why household gas (propane) in the event of a leak accumulates in the basement of houses, forming an explosive mixture there.

Heat of combustion

Heat of combustion or calorific value- the amount of heat that is released during the complete combustion of 1 m 3 of gas. On average, it is 35160 kJ / m 3 (kilojoules per 1 m 3).

Gas solubility

Solubility in oil

The solubility of gas in oil depends on the pressure, temperature and composition of the oil and gas. As the pressure increases, the solubility of the gas also increases. As the temperature rises, the solubility of the gas decreases. Low molecular weight gases are more difficult to dissolve in oils than fatter ones.

With an increase in oil density, i.e. as the content of macromolecular compounds in it increases, the solubility of the gas in it decreases.

An indicator of the solubility of gas in oil is the gas factor - G, which shows the amount of gas in 1 m 3 (or 1 ton) of degassed oil. It is measured in m 3 / m 3 or m 3 / t.

According to this indicator, deposits are divided into:

1) oil - G<650 м 3 /м 3 ;

2) oil with a gas cap - G-650 - 900 m 3 / m 3;

3) gas condensate - G>900 m 3 /m 3.

Solubility of water in compressed gas

Water dissolves in compressed gas at high pressure. This pressure makes it possible to move water in the subsoil not only in the liquid, but also in the gas phase, which ensures its greater mobility and permeability through rocks. As the mineralization of water increases, its solubility in the gas decreases.

Solubility of liquid hydrocarbons in compressed gases

Liquid hydrocarbons dissolve well in compressed gases, creating gas condensate mixtures. This creates the possibility of transfer (migration) of liquid hydrocarbons in the gas phase, providing an easier and faster process of its movement through the rock mass.

With increasing pressure and temperature, the solubility of liquid hydrocarbons in gas increases.

Compressibility

Formation gas compressibility is a very important property of natural gases. The volume of gas in reservoir conditions is 2 orders of magnitude (ie, approximately 100 times) less than its volume under standard conditions on the earth's surface. This is because the gas has a high degree of compressibility at high pressures and temperatures.

The degree of compressibility is depicted in terms of the reservoir gas volume ratio, which is the ratio of the volume of gas in reservoir conditions to the volume of the same amount of gas under atmospheric conditions.

Condensate formation is closely related to the phenomena of compressibility of gases and the solubility of liquid hydrocarbons in them. In reservoir conditions, with increasing pressure, liquid components pass into a gaseous state, forming "gas-dissolved oil" or gas condensate. When the pressure drops, the process goes in the opposite direction, i.e. partial condensation of a gas (or vapor) into a liquid state. Therefore, during gas production, condensate is also extracted to the surface.

Condensate factor

The condensate factor - CF - is the amount of raw condensate in cm 3 per 1 m3 of separated gas.

Distinguish between raw and stable condensate. Raw condensate is a liquid phase in which gaseous components are dissolved.

Stable condensate is obtained from crude by its degassing. It consists only of liquid hydrocarbons - pentane and higher.

Under standard conditions, gas condensates are colorless liquids with a density of 0.625 - 0.825 g / cm 3 with an initial boiling point from 24 0 C to 92 0 C. Most of the fractions have a boiling point up to 250 0 C.

A gas is a comparison of the relative molecular or molar mass of one gas with that of another gas. As a rule, it is defined in relation to the light gas- hydrogen. Gases are also often compared to air.

In order to show which gas is selected for comparison, an index is added before the symbol of the relative density of the test, and the name itself is written in brackets. For example, DH2(SO2). This means that the density was calculated from hydrogen. This is read as "the density of sulfur oxide by hydrogen."

To calculate the gas density from hydrogen, it is necessary to determine the molar masses of the gas and hydrogen under study using the periodic table. If it is chlorine and hydrogen, then the indicators will look like this: M (Cl2) \u003d 71 g / mol and M (H2) \u003d 2 g / mol. If the density of hydrogen is divided by the density of chlorine (71:2), the result is 35.5. That is, chlorine is 35.5 times heavier than hydrogen.

The relative density of a gas does not depend on external conditions. This is explained by the universal laws of the state of gases, which boil down to the fact that a change in temperature and pressure does not lead to a change in their volume. With any changes in these indicators, measurements are made in exactly the same way.

To determine the density of a gas empirically, you need a flask where it can be placed. The flask with gas must be weighed twice: the first time - after pumping out all the air from it; the second - by filling it with the investigated gas. It is also necessary to measure the volume of the flask in advance.

First you need to calculate the mass difference and divide it by the value of the volume of the flask. The result is the density of the gas under the given conditions. Using the equation of state, you can calculate the desired indicator for normal or ideal conditions.

You can find out the density of some gases from the summary table, which has ready-made information. If the gas is listed in the table, then this information can be taken without any additional calculations and the use of formulas. For example, the density of water vapor can be found from the table of properties of water (Reference book by Rivkin S.L. and others), its electronic counterpart, or using programs such as WaterSteamPro and others.

However, for different liquids, equilibrium with vapor occurs at different densities of the latter. This is due to the difference in the forces of intermolecular interaction. The higher it is, the faster the equilibrium will come (for example, mercury). In volatile liquids (for example, ether), equilibrium can only occur at a significant vapor density.

The density of various natural gases varies from 0.72 to 2.00 kg/m3 and above, relative - from 0.6 to 1.5 and above. The highest density is in gases with the highest content of heavy hydrocarbons H2S, CO2 and N2, the lowest is in dry methane gases.

Properties are determined by its composition, temperature, pressure and density. The last indicator is determined by the laboratory. It depends on all of the above. You can determine its density different methods. The most accurate is weighing on accurate scales in a thin-walled glass container.

More than the same indicator of natural gases. In practice, this ratio is taken as 0.6:1. Static decreases faster than gas. At pressures up to 100 MPa, the density of natural gas can exceed 0.35 g/cm3.

It has been established that the increase may be accompanied by an increase in the temperature of hydrate formation. Low density natural gas forms hydrates at a higher temperature than higher density gases.

Density meters are just beginning to be used and there are still many questions that are related to the features of their operation and verification.

Instruction

In order to cope with the task, it is necessary to use the formulas on the relative density:

First, find the relative molecular weight of ammonia, which can be calculated from the table D.I. Mendeleev.

Ar (N) = 14, Ar (H) = 3 x 1 = 3, hence
Mr(NH3) = 14 + 3 = 17

Substitute the obtained data into the formula for determining the relative density by air:
D (air) = Mr (ammonia) / Mr (air);
D (air) = Mr (ammonia) / 29;
D (air) = 17/ 29 = 0.59.

Example No. 2. Calculate the relative density of ammonia with respect to hydrogen.

Substitute the data in the formula for determining the relative density for hydrogen:
D (hydrogen) = Mr (ammonia) / Mr (hydrogen);
D (hydrogen) = Mr (ammonia) / 2;
D (hydrogen) = 17/ 2 = 8.5.

Hydrogen (from the Latin "Hydrogenium" - "generating water") is the first element of the periodic table. It is widely distributed, exists in the form of three isotopes - protium, deuterium and tritium. Hydrogen is a light colorless gas (14.5 times lighter than air). It is highly explosive when mixed with air and oxygen. Used in chemical Food Industry, as well as rocket fuel. Research is underway on the possibility of using hydrogen as fuel for automotive engines. Density hydrogen(as well as any other gas) can be defined different ways.

Instruction

First, based on the universal definition of density - the amount of substance per unit volume. In the event that it is in a sealed vessel, the density of the gas is determined elementarily, according to the formula (M1 - M2) / V, where M1 is the total mass of the vessel with gas, M2 is the mass of the empty vessel, and V is the internal volume of the vessel.

If you want to determine the density hydrogen, having such initial data as , here the universal equation of state of an ideal gas comes to the rescue, or the Mendeleev-Clapeyron equation: PV = (mRT)/M.
P - gas pressure
V is its volume
R is the universal gas constant
T is the gas temperature in Kelvin
M is the molar mass of the gas
m is the actual mass of gas.

An ideal gas is considered to be such a mathematical gas in which the potential energy of molecules compared to their kinetic energy can be neglected. In the ideal gas model, there are no attractive or repulsive forces between molecules, and the collisions of particles with other particles or vessel walls are absolutely elastic.

Of course, neither hydrogen nor any other gas is ideal, but this model allows calculations with sufficiently high accuracy at close to atmospheric pressure and room temperature. For example, given the task: find the density hydrogen at a pressure of 6 and a temperature of 20 degrees Celsius.

First, convert all initial values ​​​​to the SI system (6 atmospheres \u003d 607950 Pa, 20 degrees C \u003d 293 degrees K). Then write the Mendeleev-Clapeyron equation PV = (mRT)/M. Convert it to: P = (mRT)/MV. Since m / V is the density (the ratio of the mass of a substance to its volume), you get: density hydrogen= PM/RT, and we have all the necessary data for the solution. You know pressure (607950), temperature (293), universal gas constant (8.31), molar mass hydrogen (0,002).

Substituting this data into the formula, you get: density hydrogen under given conditions of pressure and temperature is 0.499 kg / cubic meter, or about 0.5.

Sources:

• how to find the density of hydrogen

Density- this is one of the characteristics of a substance, the same as mass, volume, temperature, area. It is equal to the ratio of mass to volume. The main task is to learn how to calculate this value and know what it depends on.

Instruction

Density is the ratio of the mass to the volume of a substance. If you want to determine the density of a substance, and you know its mass and volume, finding the density will not be difficult for you. The easiest way to find the density in this case is p = m/V. It is in kg/m^3 in the SI system. However, these two values ​​are not always given, so you should know several ways in which you can calculate the density.

Density It has different meanings depending on the type of substance. In addition, the density varies with the degree of salinity and temperature. As the temperature decreases, the density increases, and as the degree of salinity decreases, the density also decreases. For example, the density of the Red Sea is still considered high, while it is already less in the Baltic Sea. Have you all noticed that if you add water to it, it floats. All this is due to the fact that it has a lower density than water. Metals and stone substances, on the contrary, sink, since their density is higher. Based on the density of bodies arose about their swimming.

Thanks to the theory of floating bodies, by which you can find the density of a body, water, the volume of the whole body and the volume of its immersed part. This formula looks like: Vimmersed. parts / V body \u003d p body / p liquid. It follows that the density of the body can be found as follows: p body \u003d V immersed. parts * p liquid / V body. This condition is satisfied based on the tabular data and the specified volumes V immersed. parts and V body.

Related videos

Tip 4: How to calculate the relative molecular weight of a substance

Relative molecular weight is a dimensionless value showing how many times the mass of a molecule is greater than 1/12 of the mass of a carbon atom. Accordingly, the mass of a carbon atom is 12 units. Determine Relative Molecular Weight chemical compound It can be done by adding the masses of the atoms that make up a molecule of matter.

You will need

• - pen;
• - note paper;
• - calculator;
• - periodic table.

Instruction

Find in the periodic table the cells of the elements that make up this molecule. The values ​​of relative atomic masses (Ar) for each substance are indicated in the lower left corner of the cell. Rewrite them rounded to the nearest whole number: Ar(H) - 1; Ar(P) - 31; Ar(O) - 16.

Determine the relative molecular weight of the compound (Mr). To do this, multiply atomic mass each element by the number of atoms in . Then add up the resulting values. For phosphoric acid: Mr(n3po4) = 3*1 + 1*31 + 4*16 = 98.

The relative molecular weight is numerically the same as the molar mass of the substance. Some tasks use this link. Example: a gas at a temperature of 200 K and a pressure of 0.2 MPa has a density of 5.3 kg/m3. Determine its relative molecular weight.

Use the Mendeleev-Claiperon equation for an ideal gas: PV = mRT/M, where V is the gas volume, m3; m is the mass of a given volume of gas, kg; M is the molar mass of the gas, kg/mol; R is the universal gas constant. R=8.314472 m2kg s-2 K-1 Mol-1; T – gas, K; P - absolute pressure, Pa. Express the molar mass from this relationship: М = mRT/(PV).

As you know, density: p = m/V, kg/m3. Substitute it into the expression: M = pRT / P. Determine the molar mass of the gas: M \u003d 5.3 * 8.31 * 200 / (2 * 10 ^ 5) \u003d 0.044 kg / mol. Relative molecular weight of the gas: Mr = 44. You can guess that it is carbon dioxide: Mr(CO2) = 12 + 16*2 = 44.

Sources:

• calculate relative molecular weights

In chemical laboratories and during chemical experiments at home, it is often necessary to determine the relative density of a substance. Relative density is the ratio of the density of a particular substance to the density of another under certain conditions, or to the density of a reference substance, which is taken as distilled water. The relative density is expressed as an abstract number.

You will need

• - tables and directories;
• - hydrometer, pycnometer or special scales.

Instruction

The relative density of substances in relation to the density of distilled water is determined by the formula: d=p/p0, where d is the desired relative density, p is the density of the test substance, p0 is the density of the reference substance. The last parameter is tabular and is determined quite accurately: at 20 ° C, water has a density of 998.203 kg / m3, and it reaches its maximum density at 4 ° C - 999.973 kg / m3. Before calculations, do not forget that p and p0 must be expressed in the same units.

In addition, the relative density of a substance can be found in physical and chemical reference books. The numerical value of the relative density is always equal to the relative specific gravity of the same substance under the same conditions. Conclusion: use relative tables specific gravity just as if they were tables of relative density.

When determining relative density, always take into account the temperature of the test and reference substances. The fact is that the density of substances decreases with and increases with cooling. If the temperature of the test substance differs from the reference, make a correction. Calculate it as the average change in relative density per 1°C. Look for the necessary data on the nomograms of temperature corrections.

To quickly calculate the relative density of liquids in practice, use a hydrometer. Use pycnometers and special scales to measure relative and dry matter. The classic hydrometer is a glass tube that expands at the bottom. At the lower end of the tube there is a reservoir or a special substance. The upper part of the tube is marked with divisions showing the numerical value of the relative density of the test substance. Many hydrometers are additionally equipped with thermometers for measuring the temperature of the test substance.

Avogadro's Law

Distance of molecules gaseous substance from each other depends on external conditions: pressure and temperature. With the same external conditions the gaps between the molecules of different gases are the same. Avogadro's law, discovered in 1811, states that equal volumes of different gases under the same external conditions (temperature and pressure) contain the same number molecules. Those. if V1=V2, T1=T2 and P1=P2, then N1=N2, where V is volume, T is temperature, P is pressure, N is the number of gas molecules (index "1" for one gas, "2" for another).

First corollary of Avogadro's law, molar volume

The first corollary of Avogadro's law states that the same number of molecules of any gases under the same conditions occupies the same volume: V1=V2 at N1=N2, T1=T2 and P1=P2. The volume of one mole of any gas (molar volume) is a constant value. Recall that 1 mole contains the Avogadrian number of particles - 6.02x10^23 molecules.

Thus, the molar volume of a gas depends only on pressure and temperature. Normally gases are considered at normal pressure and normal temperature: 273 K (0 degrees Celsius) and 1 atm (760 mm Hg, 101325 Pa). Under such normal conditions, denoted "n.o.", the molar volume of any gas is 22.4 l / mol. Knowing this value, it is possible to calculate the volume of any given mass and any given amount of gas.

The second consequence of Avogadro's law, the relative densities of gases

To calculate the relative densities of gases, the second consequence of Avogadro's law is applied. By definition, the density of a substance is the ratio of its mass to its volume: ρ=m/V. For 1 mole of a substance, the mass is equal to the molar mass M, and the volume is equal to the molar volume V(M). Hence the density of the gas is ρ=M(gas)/V(M).

Let there be two gases - X and Y. Their densities and molar masses - ρ(X), ρ(Y), M(X), M(Y), interconnected by the relations: ρ(X)=M(X)/ V(M), ρ(Y)=M(Y)/V(M). The relative density of gas X over gas Y, denoted as Dy(X), is the ratio of the densities of these gases ρ(X)/ρ(Y): Dy(X)=ρ(X)/ρ(Y)=M(X)xV( M)/V(M)xM(Y)=M(X)/M(Y). The molar volumes are reduced, and from this we can conclude that the relative density of gas X over gas Y is equal to the ratio of their molar or relative molecular masses (they are numerically equal).

The densities of gases are often determined in relation to hydrogen, the lightest of all gases, the molar mass of which is 2 g / mol. Those. if the problem says that the unknown gas X has a hydrogen density of, say, 15 (relative density is a dimensionless quantity!), then finding its molar mass is not difficult: M(X)=15xM(H2)=15x2=30 g/ mol. Often the relative density of the gas relative to air is also indicated. Here you need to know that the average relative molecular weight of air is 29, and you already need to multiply not by 2, but by 29.

The density is called physical quantity, which determines the ratio of the mass of an object, substance or liquid to the volume they occupy in space. Let's talk about what density is, how the density of a body and matter differs, and how (using what formula) to find density in physics.

Types of density

It should be clarified that the density can be divided into several types.

Depending on the object under study:

• The density of a body - for homogeneous bodies - is the direct ratio of the mass of the body to its volume occupied in space.
• The density of a substance is the density of bodies consisting of this substance. The density of substances is constant. There are special tables where the density is indicated different substances. For example, the density of aluminum is 2.7 * 103 kg / m 3. Knowing the density of aluminum and the mass of the body that is made of it, we can calculate the volume of this body. Or, knowing that the body consists of aluminum and knowing the volume of this body, we can easily calculate its mass. How to find these values, we will consider a little later, when we derive a formula for calculating the density.
• If the body consists of several substances, then to determine its density, it is necessary to calculate the density of its parts for each substance separately. This density is called the average density of the body.

Depending on the porosity of the substance of which the body is composed:

• True density is the density that is calculated without taking into account the voids in the body.
• Specific gravity- or apparent density - this is the one that is calculated taking into account the voids of a body consisting of a porous or friable substance.

So how do you find density?

Density Formula

The formula to help find the density of a body is as follows:

• p = m / V, where p is the density of the substance, m is the mass of the body, V is the volume of the body in space.

If we calculate the density of a particular gas, then the formula will look like this:

• p \u003d M / V m p is the density of the gas, M is the molar mass of the gas, V m is the molar volume, which under normal conditions is 22.4 l / mol.

Example: the mass of a substance is 15 kg, it occupies 5 liters. What is the density of matter?

Solution: Substitute the values ​​into the formula

• p = 15 / 5 = 3 (kg/l)

Answer: the density of the substance is 3 kg / l

Density units

In addition to knowing how to find the density of a body and a substance, it is also necessary to know the units of density measurement.

• For solids- kg / m 3, g / cm 3
• For liquids - 1 g / l or 10 3 kg / m 3
• For gases - 1 g / l or 10 3 kg / m 3

You can read more about density units in our article.

How to find density at home

In order to find the density of a body or substance at home, you will need:

1. Scales;
2. centimeter if the body is solid;
3. Vessel, if you want to measure the density of a liquid.

To find the density of a body at home, you need to measure its volume with a centimeter or vessel, and then put the body on the scales. If you're measuring the density of a liquid, don't forget to subtract the mass of the vessel into which you poured the liquid before calculating. It is much more difficult to calculate the density of gases at home, we recommend using ready-made tables in which the densities of various gases are already indicated.

ρ = m (gas) / V (gas)

D by Y (X) \u003d M (X) / M (Y)

So:
D by air. = M (gas X) / 29

Dynamic and kinematic viscosity of gas.

The viscosity of gases (the phenomenon of internal friction) is the appearance of friction forces between gas layers moving relative to each other in parallel and at different velocities.
The interaction of two layers of gas is considered as a process during which momentum is transferred from one layer to another.
The force of friction per unit area between two layers of gas, equal to the momentum transferred per second from layer to layer through a unit area, is determined by Newton's law:

Velocity gradient in the direction perpendicular to the direction of motion of the gas layers.
The minus sign indicates that momentum is carried in the direction of decreasing velocity.
- dynamic viscosity.
, where
is the density of the gas,
- arithmetic average speed of molecules,
- average length free path of molecules.

Kinematic coefficient of viscosity.

Critical gas parameters: Тcr, Рcr.

The critical temperature is the temperature above which, at any pressure, the gas cannot be transferred to the liquid state. The pressure required to liquefy a gas at a critical temperature is called critical pressure. Given gas parameters. The given parameters are dimensionless quantities that show how many times the actual parameters of the state of the gas (pressure, temperature, density, specific volume) are greater or less than the critical ones:

Downhole production and underground gas storage.

Gas density: absolute and relative.

The density of a gas is one of its most important characteristics. Speaking of the density of a gas, one usually means its density under normal conditions (i.e., at temperature and pressure). In addition, the relative density of a gas is often used, by which is meant the ratio of the density of a given gas to the density of air under the same conditions. It is easy to see that the relative density of a gas does not depend on the conditions in which it is located, since, according to the laws of the gaseous state, the volumes of all gases change with changes in pressure and temperature in the same way.

The absolute density of a gas is the mass of 1 liter of gas under normal conditions. Usually for gases it is measured in g / l.

ρ = m (gas) / V (gas)

If we take 1 mole of gas, then:

and the molar mass of a gas can be found by multiplying the density by the molar volume.

Relative density D is a value that shows how many times gas X is heavier than gas Y. It is calculated as the ratio of the molar masses of gases X and Y:

D by Y (X) \u003d M (X) / M (Y)

Often, the relative densities of gases for hydrogen and for air are used for calculations.

Relative gas density X for hydrogen:

D by H2 = M (gas X) / M (H2) = M (gas X) / 2

Air is a mixture of gases, so only the average molar mass can be calculated for it.

Its value is taken as 29 g/mol (based on the approximate average composition).
So:
D by air. = M (gas X) / 29

Gas density B (pw, g / l) is determined by weighing (mv) a small glass flask of a known volume with gas (Fig. 274, a) or a gas pycnometer (see Fig. 77), using the formula

where V is the volume of the cone (5 - 20 ml) or pycnometer.

The cone is weighed twice: first evacuated and then filled with the gas under investigation. By the difference in the values ​​​​of the 2 masses obtained, the mass of the gas mv, g is recognized. When filling the cone with gas, its pressure is measured, and when weighed, the temperature environment, which is taken as the temperature of the gas in the cone. The found values ​​of p and T of the gas make it possible to calculate the density of the gas under normal conditions (0 °C; about 0.1 MPa).

To reduce the correction for the loss of mass of a cone with gas in air when it is weighed as a container, a sealed cone of exactly the same volume is placed on the other arm of the balance beam.

Rice. 274. Devices for determining the density of a gas: a cone (a) and liquid (b) and mercury (c) effuiometers

The surface of this cone is treated (cleaned) each time in exactly the same way as that weighed with gas.

During the evacuation process, the cone is slightly heated, leaving it connected to the vacuum system for several hours, since the remaining air and moisture are difficult to remove. An evacuated cone may change volume due to compression of the walls by atmospheric pressure. The error in determining the density of light gases from such compression can reach 1%. In some cases, the relative density dv is also determined for a gas, i.e. the ratio of the density of a given gas p to the density of another gas, chosen as a standard p0, taken at the same temperature and pressure:

where Mv and Mo are, respectively, the molar masses of the investigated gas B and the standard, for example, air or hydrogen, g / mol.

For hydrogen M0 = 2.016 g/mol, therefore

From this ratio, you can determine the molar mass of the gas, if we take it as ideal.

A quick method for determining the density of a gas is to measure the duration of its outflow from a small orifice under pressure, which is proportional to the outflow velocity.

where τv and τo ~ the outflow time of gas B and air, respectively.

The measurement of gas density by this method is carried out with the strip of the effusiometer (Fig. 274.6) - a wide cylinder b about 400 mm high, inside which there is a vessel 5 with a base 7 equipped with holes for the inlet and outlet of the liquid. Vessel 5 has two marks M1 and M2 for reading the volume of gas, the time of which is observed. Valve 3 serves to inlet gas, and valve 2 - to release through capillary 1. Thermometer 4 controls the temperature of the gas.

Determination of the density of the gas by the speed of its expiration is performed as follows. Cylinder b is filled with liquid, in which the gas is almost insoluble, so that vessel 5 is also filled above the mark M2. Then, through the tap 3, the liquid is squeezed out of the vessel 5 by the gas under study below the M1 mark, and all the liquid should remain in the cylinder. After that, having closed tap 3, open tap 2 and allow excess gas to escape through capillary 1. As soon as the liquid reaches the M1 mark, start the stopwatch. The liquid, displacing the gas, gradually rises to the M2 mark. At the moment the meniscus of the liquid touches the mark M2, the stopwatch is turned off. The experiment is repeated 2-3 times. Similar operations are carried out with air, thoroughly washing the vessel 5 with it from the remnants of the test gas. Different observations of the duration of the outflow of gas should not differ by more than 0.2 - 0.3 s.

If it is impossible to select a liquid for the gas under study in which it would be slightly soluble, a mercury effusion meter is used (Fig. 274, c). It consists of a glass vessel 4 with three-way valve 1 and surge vessel 5 filled with mercury. Vessel 4 is located in glass vessel 3, which functions as a thermostat. Gas is introduced through valve 1 into vessel 4, displacing mercury below the M1 mark. The test gas or air is released through the capillary 2, raising the leveling vessel 5. More sensitive devices for determining the density of gases are the Stock gas hydrometer (Fig. 275, a) and gas scales

Stock Alfred (1876-1946) - German inorganic chemist and analyst.

In the Stock hydrometer, one end of the quartz tube is inflated into a thin-walled ball 1 with a diameter of 30 - 35 mm, filled with air, and the other is pulled into a hair 7. A small iron rod 3 is tightly squeezed inside the tube.

Rice. 275. Rod hydrometer (a) and installation diagram (b)

The tip of the cut with a ball rests on a quartz or agate support. The tube with the ball is placed in a quartz vessel 5 with a polished round stopper. Outside the vessel is a solenoid 6 with an iron core. With the help of a current of various strengths flowing through the solenoid, the position of the rocker arm is aligned with the ball so that the hair 7 points exactly to the zero indicator 8. The position of the hair is observed using a telescope or microscope.

The stem hydrometer is welded to tube 2 to eliminate any vibrations.

The ball and tube are in equilibrium for a given density of the surrounding gas. If in vessel 5 one gas is replaced by another at a constant pressure, then the equilibrium will be disturbed due to a change in the density of the gas. To restore it, it is necessary either to pull the rod 3 down with an electromagnet 6 when the gas density decreases, or let it rise upwards when the density increases. The strength of the current flowing through the solenoid, when equilibrium is reached, is directly proportional to the change in density.

The instrument is calibrated for gases of known density. The accuracy of the Rod hydrometer is 0.01 - 0.1%, the sensitivity is about DO "7 g, the measurement range is from 0 to 4 g / l.

Installation with a Rod hydrometer. The stem hydrometer / (Fig-275.6) is attached to the vacuum system so that it hangs on the tube 2 as on a spring. Elbow 3 of tube 2 is immersed in a Dewar vessel 4 with a cooling mixture that allows maintaining a temperature not higher than -80 o C for condensation of mercury vapor, if a diffusion mercury pump is used to create a vacuum in the hydrometer. Valve 5 connects the hydrometer to a flask containing the gas under investigation. The trap protects the diffusion pump from exposure to the test gas, and fixture 7 serves to finely adjust the pressure. The entire system is connected to a diffusion pump through a tube.

The volume of gas is measured using calibrated gas berets (see Fig. 84) with a thermostatically controlled water jacket. In order to avoid corrections for capillary phenomena, gas 3 and compensation 5 burettes are selected with the same diameter and placed side by side in a thermostatically controlled jacket 4 (Fig. 276). Mercury, glycerin and other liquids that poorly dissolve the gas under study are used as barrier liquids.

Operate this device as follows. First, fill the burettes with liquid to a level above tap 2, raising vessel b. Then the gas burette is connected to a gas source and it is introduced, lowering vessel b, after which valve 2 is closed. To equalize the pressure of the gas in the burette 3 with atmospheric pressure, the vessel b is brought close to the burette and set at such a height that the menisci of mercury in the compensation 5 and gas 3 burettes are at the same level. Since the compensating burette communicates with the atmosphere (its upper end is open), with this position of the meniscus, the gas pressure in the gas burette will be equal to atmospheric pressure.

At the same time, atmospheric pressure is measured using a barometer and the temperature of the water in the jacket 4 using a thermometer 7.

The found volume of gas is brought to normal conditions (0 ° C; 0.1 MPa) using the equation for an ideal gas:

V0 and V are the volume (l) of gas reduced to normal conditions and the measured volume of gas at temperature t (°C), respectively; p - atmospheric pressure at the time of measuring the gas volume, torr.

If the gas contains water vapor or was before measuring the volume in a vessel above water or an aqueous solution, then its volume is brought to normal conditions, taking into account the water vapor pressure p1 at the temperature of the experiment (see Table 37):

The equations apply if the atmospheric pressure when measuring the gas volume was relatively close to 760 Torr. Pressure real gas always less than ideal, due to the interaction of molecules. Therefore, in the found value of the gas volume, a correction for the imperfection of the gas, taken from special reference books, is introduced.

Ministry of Education and Science of the Russian Federation

federal state budgetary educational institution higher professional education

"Russian State University oil and gas them. I.M. Gubkin"

A.N. Timashev, T.A. Berkunova, E.A. Mammadov

GAS DENSITY DETERMINATION

Guidelines for the implementation of laboratory work in the disciplines "Technology of operation of gas wells" and "Development and operation of gas and gas condensate fields" for students of specialties:

WG, RN, RB, MB, MO, GR, GI, GP, GF

Under the editorship of Professor A.I. Ermolaeva

Moscow 2012

Determination of gas density.

Guidelines for laboratory work / A.N. Timashev,

T.A. Berkunova, E.A. Mammadov - M.: Russian State University of Oil and Gas named after I.M. Gubkina, 2012.

Methods for laboratory determination of gas density are outlined. It is based on the current GOST 17310 - 2002.

Methodical instructions are intended for students of oil and gas universities of specialties: RG, RN, RB, MB, MO, GR, GI, GP, GF.

The publication was prepared at the Department of Development and Operation of Gas and Gas

zocondensate deposits.

Printed by decision of the educational and methodological commission of the faculty

botki oil and gas fields.

	Introduction……………………………………………………………….
	Basic Definitions……………………………………………….
	Density of natural gas at atmospheric pressure…………..
	Relative density of gas……………………………………….
	Density of natural gas at pressures and temperatures……….
	Laboratory methods for determining the density of natural gas….
	Pycnometric method………………………………………………
	Calculation formulas…………………………………………………..
	Density determination procedure……………………………………
	Calculation of gas density……………………………………………………
	Determination of gas density by the outflow method…………………..
	The derivation of relations for determining the density of the studied ha-
	behind………………………………………………………………………..
2.2.2. Order of work………………………………………….
2.2.3. Processing of measurement results…………………………………..
	Test questions………………………………………………..
	Literature…………………………………………………………….
	Annex A……………………………………………………………
	Appendix B………………………………………………………….
	Appendix B…………………………………………………………

Introduction

The physical properties of natural gases and hydrocarbon condensates are used

are used both at the design stage, development and development of the field

densities of natural gases, and in the analysis and control of field development,

operation of the system for collecting and preparing products from gas and gas condensate wells. One of the main physical properties to be studied is the gas density of the deposits.

Since the gas composition of natural gas fields is complex,

consisting of hydrocarbons (alkanes, cycloalkanes and arenes) and non-hydrocarbons

components (nitrogen, helium and other rare earth gases, as well as acidic components

nites H2 S and CO2), there is a need for a laboratory determination of density

sti gases.

In this guidelines considered calculation methods to determine

determination of gas density according to a known composition, as well as two laboratory methods for determining gas density: pycnometric and the method of flow through a capillary

1. Basic definitions

1.1. Density of natural gas at atmospheric pressure

The density of a gas is equal to the mass M contained in a unit volume v of the substance

va. Distinguish the density of the gas at normal n P 0.1013 MPa, T 273K and

	standard with R 0.1013MPa, T 293K									under conditions, as well as at any pressure
	leniya Р and temperature Т Р,Т.									known molecular weight
	the density under normal conditions is
	under standard conditions

Where M is the molecular weight of the gas, kg/kmol; 22.41 and 24.04, m3 / kmol - the molar volume of gas, respectively, at normal (0.1013 MPa, 273 K) and standard

(0.1013 MPa, 293 K) conditions.

For natural gases consisting of hydrocarbon and non-hydrocarbon components (acidic and inert), the apparent molecular weight M to

is determined by the formula

				êã/ êì î ëü,

where M i is the molecular weight of the i-th component, kg/kmol; n i is the molar percentage of the i-th component in the mixture;

k is the number of components in the mixture (natural gas).

Density of natural gas cm is equal to

							at 0.1 MPa and 293 K
							at 0.1 MPa and 293 K

i is the density of the i-th component at 0.1 MPa and 293 K.

Data on individual components are shown in table 1.

Density conversion at various conditions temperature and pressure

0.1013 MPa (101.325 kPa) in Annex B.

1.2. Relative gas density

In the practice of engineering calculations, the concept of relative

density equal to the ratio of gas density to air density at the same values pressure and temperature. Normally, normal or standard conditions are taken as reference, while the air density is

responsibly amounts to 0 1.293 kg / m 3 and 20 1.205 kg / m 3. Then the relative

The density of natural gas is equal to

1.3. Density of natural gas at pressures and temperatures

Gas density for conditions in the reservoir, wellbore, gas

wires and devices at appropriate pressures and temperatures determine

is calculated according to the following formula

where P and T are pressure and temperature at the place where the gas density is calculated; 293 K and 0.1013 MPa - standard conditions when found cm;

z ,z 0 are the coefficients of gas supercompressibility, respectively, at Р and Т and

under standard conditions (value z 0 = 1).

The simplest way to determine the supercompressibility factor z is the graphical method. The dependence of z on the given parameters is

placed in Fig. one.

For a one-component gas (pure gas), the given parameters are determined

divided by formulas

	and T c are the critical parameters of the gas.
For multicomponent (natural) gases, pre-calculate
pseudocritical pressures and temperatures according to the dependences
	T nskn iT ci /100,
	and T c are the critical parameters of the i -th component of the gas.
Since the composition of natural gas is determined to butane C4 H10											or hexane C6 H14

inclusive, and all other components are combined into a remainder (pseudo-component

component) C5+ or C7+, in this case, the critical parameters are determined by the formula

At 100 M with 5 240 and 700d with 5 950,

М с 5 is the molecular weight of С5+ (С7+) kg/kmol;

d c 5 is the density of the С5+ (С7+) pseudo-component, kg/m3.

Relationship between M s		is found by Craig's formula

Table 1

Indicators of natural gas components

Indicators

Components

Molecular mass,

M kg/kmol

Density, kg/m3 0.1

Density, kg/m3 0.1

Relative plot-

critical volume,

dm3 /kmol

critical pressure,

Critical tempera-

Critical compression

bridge, zcr

Acentric factor

Figure 1 - Dependence of the supercompressibility factor z on the given parameters Ppr and Tpr 2. Laboratory methods for determining the density of natural gas 2.1. Pycnometric method The pycnometric method is established by the GOST 17310-2002 standard, in accordance with which determines the density (relative density) of gases and gas mixtures. The essence of the method lies in weighing a glass pycnometer with a volume of 100-200 cm3 in series with dried air and dried the next gas at the same temperature and pressure. The density of dry air is a reference value. Knowing the internal volume of the pycnometer, it is possible to determine the density of natural gas of unknown composition (test gas). To do this, the internal volume of the pycnometer (“water number”) is preliminarily determined by alternately weighing the pycnometer with dried air and distilled water, the densities of which are known. Then weigh- a pycnometer filled with the investigated gas is sewn. The difference between the masses of the pycnometer with the test gas and the pycnometer with air, divided by the value of the volume of the pycnometer ("water number") is added to the value of the density of dry air, which is the final density of the gas under study. The derivation of the calculation formulas is shown below. 2.1.1. Calculation formulas The density of natural gas is determined by the pycnometric method based on the following relationships: d is the density of the gas under measurement conditions, g/dm3 kg; vz – air density under the conditions of measurements, g/dm3 kg; Mg is the mass of gas in a pycnometer, g; Mvz is the mass of air in a pycnometer, g;