Water properties - the chemical and physical properties of liquid water. Critical point Water in critical condition

A liquid, for example water, can be in a solid, liquid and gaseous state, which are called phase states of matter... In liquids, the distance between molecules is about two orders of magnitude less than in gases. In a solid, the molecules are even closer together. Temperature at which changes phase state of matter(liquid - solid, liquid - gaseous), called phase transition temperature.

By the heat of phase transition or latent heat is the value of the heat of fusion or evaporation of a substance. Figure 6.9 shows the dependence of water temperature on the amount of heat received in calories. It can be seen that at temperatures of 0 0 C and 100 0 C, the phase state of water changes, while the water temperature does not change. The absorbed heat is spent on changing the phase state of the substance. Physically, this means that when a solid, for example, ice, is heated at 0 0 C, the amplitude of oscillations of molecules relative to each other increases. This leads to an increase in their potential energy, and, consequently, to a weakening or rupture of intermolecular bonds. Molecules or their clusters are able to move relative to each other. Ice turns into liquid at a constant temperature. After changing its state of aggregation from solid to liquid, the absorption of heat leads to an increase in temperature according to a linear law. This happens up to 100 0 C. Then the energy of the vibrating molecules increases so much that the molecules are able to overcome the attraction of other molecules. They rapidly break away not only from the surface of the water, but also form bubbles of vapor throughout the entire volume of the liquid. They rise to the surface under the action of a buoyant force and are thrown outward. In this phase transition, water turns into steam. Then again, the absorption of heat leads to an increase in the temperature of the steam according to a linear law.

The heat released or absorbed during the phase transition depends on the mass of the substance.

When a substance of mass m passes from a liquid to a gaseous state or, conversely, from a gaseous to a liquid, heat Q is absorbed or released:

Specific heat of vaporization Q required to convert 1 kg of liquid into steam at boiling point:

When a substance passes from a solid state to a liquid and back, an amount of heat is absorbed or transferred:

Specific heat of fusion q called the amount of heat Q required to convert 1 kg of a solid (for example, ice) into a liquid at the melting point:

Specific heat melting and vaporization is measured in J / kg. With an increase in temperature, the specific heat of vaporization decreases, and with critical temperature becomes zero.

For water, the specific heat of fusion and vaporization, respectively, are:

, .

It uses a non-systemic unit for measuring the amount of energy - a calorie, equal to the amount of heat required to heat 1 gram of water by 1 ° C at a normal atmospheric pressure of 101.325 kPa.

As can be seen in Figure 6.17, heating ice from -20 0 С to 0 0 С requires eight times less energy than converting it from ice into water, and 54 times less than converting water into steam.

Figure 6.17. Dependence of temperature on the heat supplied to the system

for 1 kg of ice.

The temperature at which the difference between vapor and liquid is lost is called critical... In fig. 6.18 illustrates the concept of critical temperature on the dependence of the density of water and steam on temperature. When water is heated in a closed test tube, as can be seen in Fig. 6.18, the water density decreases with increasing temperature due to the volumetric expansion of water, and the vapor density increases. At a certain temperature, which is called critical, the vapor density becomes equal to the density of water.

Each substance has its own critical temperature. For water, nitrogen and helium, the critical temperatures are respectively:

, , .

Figure 6.18. Critical point on the dependency graph

density of steam and water from temperature.

Figure 6.19. Dependence of pressure on volume p = p (V) for steam. In the area marked with a dotted line, the gaseous and liquid states of matter exist simultaneously.

Figure 6.19 shows the dependence of the vapor pressure on its volume P = P (V). The equation of state of vapor at low pressure and far from the temperature of its phase transition (above the point b 0 in Figure 6.19) is close to the equation of state for an ideal gas (that is, in this case, the gas can be considered ideal and its behavior is well described by the Boyle-Moriott law). With decreasing temperature, the dependence Р = Р (V) begins to differ from its form for an ideal gas. Location on a - b vapor condensation occurs and the vapor pressure remains almost unchanged, and the dependence in Fig. 6.19 is a slowly decreasing linear function. Below the point a, all the vapor becomes a liquid, and then the liquid is already compressed. In this case, as can be seen in Fig. 6.11, the pressure increases sharply with a very slight decrease in volume, since the liquid is practically incompressible.

Since the temperature of the phase transition depends on the gas pressure, it is possible to represent the phase transitions using the dependence of pressure on temperature P = P (T) in Fig. 6.20. A change in the phase state of a substance occurs at the vapor - liquid interface, solid- liquid, solid - steam. On different sides of these boundary lines, the gas is in a different state of aggregation - solid, liquid or gaseous.

Figure 6.20. Phase diagram for water.

The intersection of the three lines in Figure 6.12 is called triple point... For example, water at a temperature of 0 0 C and a pressure of atm., Has a triple point, and carbon dioxide has a triple point at a temperature and pressure of P = 5.1 atm. Figure 6.20 shows that a transition of a substance from a gaseous to a solid state and vice versa is possible, bypassing the liquid stage.

The transition from a solid state of a substance to a gaseous state is called sublimation.

Example: cooling with dry ice, such as ice cream packs on trays. In this case, as we have seen many times, dry ice turns into steam.

Equation of state Thermodynamic quantities Thermodynamic potentials Thermodynamic cycles Phase transitions see also "Physical portal"

Critical phase transition temperature is the temperature value at the critical point. At temperatures above the critical temperature, the gas cannot be condensed at any pressure.

Physical significance

At the critical point, the density of the liquid and its saturated vapor become equal, and the surface tension of the liquid drops to zero, therefore, the liquid-vapor phase boundary disappears.

For a mixture of substances, the critical temperature is not a constant value and can be represented by a spatial curve (depending on the proportion of the constituent components), the extreme points of which are the critical temperatures of pure substances - the components of the mixture under consideration.

The critical point on the state diagram of a substance corresponds to the limiting points on the phase equilibrium curves; in the vicinity of the point, phase equilibrium is violated, and there is a loss of thermodynamic stability with respect to the density of the substance. On one side of the critical point, the substance is homogeneous (usually at texvc not found; See math / README for setup help.): T> T_ (crit)), and on the other - it is divided into liquid and vapor.

In the vicinity of the point, critical phenomena are observed: due to an increase in the characteristic sizes of density fluctuations, the scattering of light increases sharply when passing through a substance - when the size of fluctuations reaches the order of hundreds of nanometers, i.e., light wavelengths, the substance becomes opaque - its critical opalescence is observed. An increase in fluctuations also leads to an increase in the absorption of sound and an increase in its dispersion, a change in the nature of Brownian motion, anomalies in viscosity, thermal conductivity, a slowdown in the establishment of thermal equilibrium, etc.

History

For the first time, the phenomenon of the critical state of matter was discovered in 1822 by Charles Canyard de La Tour, and in 1860 it was rediscovered by D.I. Mendeleev. Systematic research began with the work of Thomas Andrews. In practice, the critical point phenomenon can be observed when heating a liquid that partially fills a sealed tube. As it heats up, the meniscus gradually loses its curvature, becoming more and more flat, and when the critical temperature is reached, it ceases to be distinguishable.

Parameters of critical points of some substances

Substance	Unable to parse expression (Executable texvc not found; See math / README for setup help.): T_ (crit)	Unable to parse expression (Executable texvc not found; See math / README for setup help.): P_ (crit)	Unable to parse expression (Executable texvc not found; See math / README for setup help.): V_ (crit)
Units	Kelvin	Atmosphere	cm³ / mol
Hydrogen	33,0	12,8	61,8
Oxygen	154,8	50,1	74,4
	1750	1500	44
Ethanol	516,3	63,0	167
Carbon dioxide	304,2	72,9	94,0
Water	647	218,3	56
Nitrogen	126.25	33,5
Argon	150.86	48,1
Bromine	588	102
Helium	5.19	2,24
Iodine	819	116
Krypton	209.45	54,3
Xenon	289.73	58
Arsenic	1673
Neon	44.4	27,2
Radon	378
Selenium	1766
Sulfur	1314
Phosphorus	994
Fluorine	144.3	51,5
Chlorine	416.95	76

Critical points exist not only for pure substances, but also, in some cases, for their mixtures and determine the parameters of the loss of stability of the mixture (with phase separation) - solution (one phase). An example of such a mixture is a phenol-water mixture.

A monoisotopic gas at a critical temperature is compressed indefinitely until the electron shells of neighboring atoms overlap without increasing pressure.

The most famous formula from general relativity is the energy-mass conservation law

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- Only that they, indeed, deeply honored John, despite the fact that they had never met him. - Sever smiled. - Well, and also the fact that, after the death of Radomir and Magdalene, Qatar really had the real “Revelations” of Christ and the diaries of John, which the Roman Church tried to find and destroy at all costs. The Pope's servants tried their best to find out where the damned Cathars were hiding their most dangerous treasure ?! For, appear all this open - and history catholic church would be completely defeated. But no matter how hard the church bloodhounds tried, happiness never smiled at them ... Nothing was ever found, except for a few eyewitness manuscripts.
That is why the only way for the church to somehow save its reputation in the case of the Cathars and was only to pervert their faith and teaching so much that no one in the world could tell the truth from lies ... How easily they did it with the life of Radomir and Magdalene.
The church also claimed that the Cathars worshiped John even more than Jesus Radomir himself. Only here by John they meant “their” John, with his false Christian Gospels and the same false manuscripts ... The real John Cathars, indeed, were honored, but, as you know, he had nothing to do with Church John- “ the baptist. "
- You know, Sever, I get the impression that the church has distorted and destroyed ALL world history. Why was it necessary?
- In order not to allow a person to think, Isidora. To make people obedient and insignificant slaves, who, at their own discretion, were “forgiven” or punished by the “holy ones”. For if a person knew the truth about his past, he would be a Proud person for himself and his Ancestors and would never put on a slave collar. Without the TRUTH from the free and strong people became "slaves of God", and no longer tried to remember who they really were. This is the present, Isidora ... And, to be honest, it does not leave too bright hopes for change.
The north was very quiet and sad. Apparently, observing human weakness and cruelty for so many centuries, and seeing how the strongest perish, his heart was poisoned with bitterness and disbelief in the quick victory of Knowledge and Light ... And I so wanted to shout to him that I still believe that people will soon wake up ! .. Despite the anger and pain, despite the betrayal and weakness, I believe that the Earth, at last, will not withstand what they are doing with her children. And he will wake up ... But I realized that I would not be able to convince him, since I myself would have to die soon, fighting for this same awakening.
But I did not regret ... My life was just a grain of sand in the endless sea of ​​suffering. And I only had to fight to the end, no matter how terrible it was. Since even drops of water, falling constantly, are able to grind the strongest stone ever. So is EVIL: if people crushed it even by a grain, it would someday collapse, even if not during this lifetime. But they would return to their Earth again and see - it was THEY who helped her to withstand! .. It was THEY who helped her to become Light and Faithful. I know Sever would say that a person still does not know how to live for the future ... And I know - while this was true. But it is precisely this, in my understanding, that stopped many from making their own decisions. Because people are too accustomed to think and act, "like everyone else", not standing out and not getting in, just to live in peace.
“Forgive me for causing you so much pain, my friend. - The voice of the North interrupted my thoughts. “But I think it will help you meet your fate more easily. It will help to withstand ...
I didn't want to think about it ... Just a little more! .. After all, I still had enough time for my sad fate. Therefore, in order to change the sore subject, I started asking questions again.

The phase equilibrium curve (in the plane P, T) may end at some point (Fig. 16); such a point is called critical, and the corresponding temperature and pressure are called critical temperature and critical pressure. At temperatures higher and at pressures higher, there are no different phases, and the body is always homogeneous.

It can be said that at the critical point the difference between the two phases disappears. The concept of a critical point was first introduced by D.I.Mendeleev (1860).

In coordinates T, V, the equilibrium diagram in the presence of a critical point looks as shown in Fig. 17. As the temperature approaches its critical value, the specific volumes of the phases in equilibrium with each other approach each other and coincide at the critical point (K in Fig. 17). A diagram in the coordinates P, V has a similar form.

In the presence of a critical point between any two states of a substance, a continuous transition can be made, in which at no time does separation into two phases occur - for this it is necessary to change the state along some curve that envelopes the critical point and does not intersect the equilibrium curve anywhere. In this sense, in the presence of a critical point, the very concept of different phases becomes conditional, and it is impossible in all cases to indicate which states are one phase and which ones are another. Strictly speaking, we can speak of two phases only when they exist both simultaneously, touching each other, that is, at points lying on the equilibrium curve.

It is clear that a critical point can exist only for such phases, the difference between which is only of a purely quantitative character. Such are the liquid and gas, differing from each other only in the greater or lesser role of the interaction between the molecules.

The same phases as a liquid and a solid (crystal) or various crystalline modifications of a substance are qualitatively different from each other, since they differ in their internal symmetry. It is clear that about any property (element) of symmetry one can only say either that it exists or that it does not exist; it can appear or disappear only immediately, abruptly, and not gradually. In each state, the body will have either one or the other symmetry, and therefore you can always indicate to which of the two phases it belongs. The critical point, therefore, for such phases cannot exist, and the equilibrium curve must either go to infinity or end, intersecting with the equilibrium curves of other phases.

An ordinary phase transition point does not represent mathematically a singularity for the thermodynamic quantities of a substance. Indeed, each of the phases can exist (at least as metastable) on the other side of the transition point; thermodynamic inequalities at this point are not violated. At the transition point, the chemical potentials of both phases are equal to each other:; for each of the functions, this point is not remarkable at all.

Let us depict in the plane Р, V any isotherm of liquid and gas, i.e., the curve of the dependence of Р on V during isothermal expansion of a homogeneous body in Fig. eighteen). According to the thermodynamic inequality, there is a decreasing function V. Such a slope of the isotherms should be preserved for some distance beyond the points of their intersection with the equilibrium curve of liquid and gas (points b and sections of isotherms correspond to metastable superheated liquid and supercooled vapor, in which thermodynamic inequalities are still satisfied ( a completely equilibrium isothermal change of state between points b does not correspond, of course, to a horizontal segment on which separation into two phases occurs).

If we take into account that the points have the same ordinate P, then it is clear that both parts of the isotherm cannot pass into each other in a continuous manner, and there must be a gap between them. The isotherms end at points (c and d) at which the thermodynamic inequality is violated, i.e.

Having constructed the locus of the termination points of the liquid and gas isotherms, we obtain the battery curve, on which thermodynamic inequalities are violated (for a homogeneous body); it limits the area in which the body under no circumstances can exist as homogeneous. The regions between this curve and the phase equilibrium curve correspond to superheated liquid and supercooled steam. Obviously, at the critical point, both curves must touch each other. Of the points lying on the battery curve itself, only the critical point K corresponds to the actually existing states of a homogeneous body - the only one in which this curve comes into contact with the region of stable homogeneous states.

In contrast to the usual points of phase equilibrium, the critical point is mathematically a singular point for the thermodynamic functions of matter (the same applies to the entire AQW curve, which limits the region of existence of homogeneous states of the body). The nature of this feature and the behavior of matter near the critical point will be considered in § 153.

If a certain amount of liquid is placed in a closed vessel, then part of the liquid will evaporate and saturated vapor will be above the liquid. The pressure, and hence the density of this vapor, depends on the temperature. The vapor density is usually significantly less than the density of the liquid at the same temperature. If the temperature is raised, the density of the liquid will decrease (§ 198), while the pressure and density of the saturated vapor will increase. Table 22 shows the values ​​of the density of water and saturated water vapor for different temperatures (and, therefore, for the corresponding pressures). In fig. 497, the same data is shown in the form of a graph. The upper part of the graph shows the change in the density of the liquid depending on its temperature. As the temperature rises, the density of the liquid decreases. The lower part of the graph shows the dependence of the density of saturated steam on temperature. The vapor density increases. At the temperature corresponding to the point, the densities of the liquid and saturated vapor coincide.

Rice. 497. Dependence of the density of water and its saturated vapor on temperature

Table 22. Properties of water and its saturated steam at different temperatures

Temperature,	Saturated steam pressure,	Density of water,	Density of saturated steam,	Specific heat of vaporization,

The table shows that the higher the temperature, the smaller the difference between the density of the liquid and the density of its saturated vapor. At a certain temperature (near water at) these densities coincide. The temperature at which the densities of a liquid and its saturated vapor coincide is called the critical temperature of a given substance. In fig. 497 it corresponds to a dot. The pressure corresponding to the point is called the critical pressure. The critical temperatures of various substances vary greatly among themselves. Some of them are given in table. 23.

Table 23. Critical temperature and critical pressure of some substances

Substance	Critical temperature,	Critical pressure, atm	Substance	Critical temperature,	Critical pressure, atm
			Carbon dioxide
			Oxygen
Ethanol

What does the existence of a critical temperature indicate? What happens at even higher temperatures?

Experience shows that at temperatures higher than critical, a substance can only be in a gaseous state. If we decrease the volume occupied by vapor at a temperature above the critical one, then the vapor pressure increases, but it does not become saturated and continues to remain homogeneous: no matter how great the pressure, we will not find two states separated by a sharp boundary, as is always observed at lower temperatures due to steam condensation. So, if the temperature of any substance is higher than the critical one, then the equilibrium of the substance in the form of a liquid and vapor in contact with it is impossible at any pressure.

The critical state of matter can be observed using the device shown in Fig. 498. It consists of an iron box with windows, which can be heated higher ("air bath"), and a glass ampoule with ether inside the bath. When the bath is heated, the meniscus in the ampoule rises, becomes flatter, and finally disappears, which indicates a transition through the critical state. When the bath is cooled, the ampoule suddenly becomes cloudy due to the formation of many tiny ether droplets, after which the ether collects in the lower part of the ampoule.

Rice. 498. A device for observing the critical state of the ether

As you can see from the table. 22, as the critical point is approached, the specific heat of vaporization becomes less and less. This is explained by the fact that as the temperature rises, the difference between the internal energies of matter in the liquid and vapor states decreases. Indeed, the adhesion forces of molecules depend on the distances between the molecules. If the densities of the liquid and vapor differ little, then the average distances between the molecules also differ little. Consequently, in this case, the values ​​of the potential energy of interaction of molecules will also differ little. The second term of the heat of vaporization - work against external pressure - also decreases as the critical temperature is approached. This follows from the fact that the smaller the difference in the densities of vapor and liquid, the smaller the expansion that occurs during evaporation, and, therefore, the less work done during evaporation.

The existence of a critical temperature was first pointed out in 1860. Dmitry Ivanovich Mendeleev (1834-1907), Russian chemist who discovered the fundamental law of modern chemistry - the periodic law chemical elements... Great service in the study of critical temperature belongs to the English chemist Thomas Andrews, who made a detailed study of the behavior of carbon dioxide during isothermal changes in the volume occupied by it. Andrews showed that at temperatures below, in a closed vessel, carbon dioxide can coexist in liquid and gaseous states; at temperatures above such coexistence is impossible and the entire vessel is filled only with gas, no matter how to reduce its volume.

After the discovery of the critical temperature, it became clear why it took a long time to turn gases such as oxygen or hydrogen into liquid. Their critical temperature is very low (Table 23). To convert these gases to liquid, they need to be cooled below a critical temperature. Without this, all attempts to liquefy them are doomed to failure.

Supercritical condition- the fourth form of the state of aggregation, into which many organic and inorganic substances are capable of passing.

For the first time, the supercritical state of matter was discovered by Canyar de la Tour in 1822. The real interest in the new phenomenon arose in 1869 after the experiments of T. Andrews. Carrying out experiments in thick-walled glass tubes, the scientist investigated the properties CO 2 which liquefies easily when the pressure rises. As a result, he found that at 31 ° C and 7.2 MPa, the meniscus - the boundary separating the liquid and the vapor in equilibrium with it, disappears, while the system becomes homogeneous (uniform) and the entire volume takes on the form of a milky-white opalescent liquid. With a further increase in temperature, it quickly becomes transparent and mobile, consisting of constantly flowing jets, reminiscent of streams of warm air over a heated surface. Further increase in temperature and pressure did not lead to visible changes.

He called the point at which such a transition occurs critical, and the state of the substance above this point - supercritical. Despite the fact that outwardly this state resembles a liquid, it is now used in application to it special term- supercritical fluid (from english word fluid, that is, "capable of flowing"). In modern literature, the abbreviated designation for supercritical fluids is accepted - SCF.

The location of the lines delimiting the regions of the gaseous, liquid and solid states, as well as the position of the triple point, where all three regions converge, are individual for each substance. The supercritical region begins at the critical point (indicated by an asterisk), which is certainly characterized by two parameters - temperature ( T cr.) and pressure ( P cr.). Lowering either temperature or pressure below critical values ​​brings the substance out of the supercritical state.

The fact of the existence of a critical point made it possible to understand why some gases, for example, hydrogen, nitrogen and oxygen, for a long time could not be obtained in liquid form with increasing pressure, which is why they were called permanent gases (from Latin permanentis- "constant"). The diagram above shows that the region of existence of the liquid phase is located to the left of the critical temperature line. Thus, in order to liquefy any gas, it must first be cooled to a temperature below the critical one. Have CO 2 the critical temperature is above room temperature, so it can be liquefied under the specified conditions by increasing the pressure. For nitrogen, the critical temperature is much lower: –146.95 ° C, therefore, if you compress nitrogen under normal conditions, you can eventually reach the supercritical region, but liquid nitrogen cannot be formed. It is necessary to first cool the nitrogen below the critical temperature and then, by increasing the pressure, reach the area where the liquid can exist. The situation is similar for hydrogen, oxygen, therefore, before liquefaction, they are cooled to a temperature below the critical one, and only then the pressure is increased. The supercritical state is possible for most substances, it is only necessary that the substance does not decompose at a critical temperature. In comparison with the indicated substances, the critical point of water is reached with great difficulty: t cr= 374.2 ° C and P cr = 21,4 MPa.

The critical point is recognized as an important physical parameter of a substance, the same as the melting or boiling point. The density of GFR is extremely low, for example, water in the GFR state has a density three times lower than under normal conditions. All SCFs are extremely low viscosity.

Supercritical fluids are a cross between liquid and gas. They can compress like gases (ordinary liquids are practically incompressible) and, at the same time, are able to dissolve many substances in solid and liquid states, which is unusual for gases. Supercritical ethanol (at temperatures above 234 ° C) very easily dissolves some inorganic salts ( CoCl 2, KBr, KI). Carbon dioxide, nitrous oxide, ethylene and some other gases in the SCF state acquire the ability to dissolve many organic substances - stearic acid, paraffin, naphthalene. Supercritical properties CO 2 as a solvent, it can be controlled - with increasing pressure, its dissolving ability increases sharply.

Supercritical fluids became widely used only in the 1980s, when general industrial development made SCF plants widely available. From that moment on, the intensive development of supercritical technologies began. SCF is not only good solvents, but also substances with a high diffusion coefficient, i.e. they easily penetrate deep layers of various solids and materials. The most widely used supercritical CO 2, which turned out to be a solvent for a wide range of organic compounds. Carbon dioxide has become a leader in the world of supercritical technology, because has a whole range of advantages. It is quite easy to transfer it to a supercritical state ( t cr- 31 ° C, P cr – 73,8 atm.), in addition, it is non-toxic, non-flammable, non-explosive, moreover, it is cheap and affordable. From the point of view of any technologist, it is the ideal component of any process. It is especially attractive because it is an integral part of atmospheric air and, therefore, does not pollute environment... Supercritical CO 2 can be considered an environmentally friendly solvent. Here are just some examples of its use.

Caffeine is a drug used to improve performance of cardio-vascular system are obtained from coffee beans even without their preliminary grinding. The completeness of extraction is achieved due to the high penetrating ability of the GFR. The grains are placed in an autoclave - a container that can withstand increased pressure, then a gaseous CO 2, then create the required pressure (> 73 atm.), as a result CO 2 goes into a supercritical state. The entire contents are mixed, after which the fluid, together with the dissolved caffeine, is poured into an open container. Carbon dioxide, being at atmospheric pressure, turns into gas and escapes into the atmosphere, while the extracted caffeine remains in an open container in its pure form.

The use of SCF has proven to be very successful in cleaning electronic circuits from contamination during their manufacture, since they do not leave any traces of cleaning solvent on them.

In connection with the rapid development of the active part of light oil reserves, interest in enhanced oil recovery methods has sharply increased. If in the 70-80s of the XX century the number of projects aimed at solving the problem of increasing oil recovery by means of injection of miscible hydrocarbon solvents, "inert" gases and carbon dioxide was comparable, then at the end of the XX and early XXI centuries only injection method CO 2 had a steady growth trend. Effectiveness of application CO 2 for enhanced oil recovery has been proven not only by experimental and theoretical works, but also by the results of numerous industrial tests.

Do not forget that enhanced oil recovery technology using CO 2 allows you to simultaneously solve the problem of conservation of a huge amount of carbon dioxide emitted by the industry.

Features of the process of impact of injected CO 2 for oil and gas deposits depend on its state of aggregation.

Excess pressure and temperature above the critical values ​​for carbon dioxide (and this is the most likely situation in reservoir conditions), predetermines its supercritical state. In this case CO 2, which has an exceptional dissolving ability in relation to hydrocarbon fluids when directly dissolved in reservoir oil, reduces its viscosity and dramatically improves filtration properties. This circumstance gives every reason to classify SCF, an enhanced oil recovery technology, as one of the most promising.

CHAPTER IV.
THERMODYNAMICS OF SOLUTIONS (SOLUTIONS)