Body temperature is one of the most important factors that are necessary for metabolism. It is an indicator of the state of the body and changes depending on the influence of external and internal factors. If you feel unwell and have a critical temperature, you must urgently contact a specialized institution. After all, this can be a harbinger of many diseases.
Factors affecting body temperature
It changes due to the influence of various factors, both the environment and the internal characteristics of the body, for example:
Subacute.
Chronic.
Times of Day. The temperature changes very often due to changes in the time of day. In this regard, in the morning the body temperature may be slightly lower (by 0.4-0.7 degrees), but not lower than +35.9°C. In the evening, on the contrary, the temperature may rise slightly (by 0.2-0.6 degrees), but not higher than +37.2°C.
Age. In children, the temperature is most often higher than 36.6 degrees, and in adults who are over 60-65 years old, the usual temperature drops.
Health status. If there is an infection in the human body, the temperature (to fight it) rises.
Pregnancy. In early pregnancy, the temperature should not fall below 36 degrees and rise above 37.5 degrees.
Individual characteristics of the body.
Environmental influence.
Classification of body temperature
If you analyze different thermometer readings, temperature can be divided into several types and classifications.
Types of temperature according to one of the classifications (according to the level of hyperthermia):
Low and reduced. The thermometer reading is below 35°C.
Normal. The value on the thermometer is within 35-37°C.
Subfebrile. The value on the thermometer is within 37-38°C.
Febrile. The value on the thermometer is within 38-39°C.
Pyretic. The value on the thermometer is within 39-41°C.
Hyperpyretic. The thermometer reading is above 41°C.
Temperature division depending on duration:
Another classification of temperature types:
Hypothermia - low body temperature (less than 35°C).
Normal temperature. This type of body temperature fluctuates between 35-37°C and varies from many factors discussed above.
Hyperthermia - increased body temperature (above 37°C).
Body temperature is within normal limits
The average body temperature, as mentioned above, can change under the influence of various factors. It can be measured not only in the armpits, but also in the mouth, ear cavity, and rectum. Depending on this, the data on the thermometer may vary; the values of critical temperatures will be much higher or lower than the standards presented here.
In the mouth, the thermometer readings will be 0.3-0.6°C higher than when measured in the armpits, that is, here the norm will be 36.9-37.2°C. In the rectum, the thermometer readings will be 0.6-1.2°C higher, that is, the norm is 37.2-37.8°C. In the ear cavity, the thermometer readings will be the same as in the rectum, that is, 37.2-37.8 ° C.
These data cannot be considered accurate for every individual. According to many studies, such indicators occur in most people - this is approximately 90%, but in 10% of people the normal body temperature differs from the majority, and the indicators can fluctuate up or down.
To find out what temperature is normal, you need to measure and record readings throughout the day: morning, afternoon and evening. After all measurements, you need to find the arithmetic mean of all indicators. To do this, you need to add the morning, afternoon and evening readings and divide by 3. The resulting number is the normal average body temperature for a particular person.
Critical body temperature
Either a very low or a very high level can become critical. High temperatures in people appear much more often than low temperatures. When the temperature drops to 26-28°C, there is a very high risk that a person will fall into a coma, problems with breathing and heart will appear, but these figures are individual, since there are many confirmed stories about how, after severe hypothermia, up to 16-17 °C people managed to survive. For example, a story that says that a man spent about five hours in a huge snowdrift without a chance to get out and survive, his temperature dropped to 19 degrees, but they were able to save him.
Low body temperature
The limit of low temperature is considered to be a temperature lower than 36 degrees, or ranging from 0.5 to 1.5 degrees below a person’s individual temperature. And the limit of low temperature is considered to be the temperature that is lower by more than 1.5 ° C from normal.
There are many reasons for a decrease in temperature, for example, decreased immunity, prolonged exposure to the cold, and based on this, hypothermia of the body, thyroid disease, stress, poisoning, chronic diseases, dizziness and even banal fatigue.
If the body temperature drops to 35°C, then you need to urgently call an ambulance, because in most cases this indicator is critical and irreversible consequences may occur!
What critical temperature should alert you?
A temperature that starts at 37 degrees is considered subfertile and often indicates the presence of inflammation, infections and viruses in the body. The temperature from 37 to 38 degrees cannot be brought down with the help of medications, because In the body there is a struggle between healthy cells and pathogenic cells.
There are many symptoms that indicate an increase in temperature, for example: weakness, fatigue, chills, headaches and muscle pain, loss of appetite and sweating. You should pay special attention to them to prevent the temperature from rising to 38.5 degrees.
The critical body temperature is 42°C, and in most cases, a mark of 40 degrees already leads to death. High temperature leads to irreversible consequences in the brain; metabolism in brain tissue is disrupted.
In this case, if the temperature rises above 38.5 degrees, bed rest, taking antipyretics, and always seeing a doctor or calling an ambulance are important! To prevent death at a very high or low temperature, do not self-medicate, but always consult a doctor who can correctly determine the cause of such a temperature, make a diagnosis and prescribe the correct and effective treatment!
How to turn gas into liquid? The boiling point chart answers this question. You can turn a gas into a liquid by either decreasing the temperature or increasing the pressure.
In the 19th century, increasing pressure seemed an easier task than lowering temperature. At the beginning of this century, the great English physicist Michael Farada managed to compress gases to vapor pressure values and in this way turn many gases (chlorine, carbon dioxide, etc.) into liquid.
However, some gases - hydrogen, nitrogen, oxygen - could not be liquefied. No matter how much pressure was increased, they did not turn into liquid. One might think that oxygen and other gases cannot be liquid. They were classified as true, or permanent, gases.
In fact, the failures were caused by a lack of understanding of one important circumstance.
Let us consider liquid and vapor in equilibrium and think about what happens to them as the boiling point increases and, of course, the corresponding increase in pressure. In other words, imagine that a point on the boiling graph moves upward along the curve. It is clear that as the temperature increases, a liquid expands and its density decreases. As for steam, does the boiling point increase? of course, contributes to its expansion, but, as we have already said, the saturated vapor pressure increases much faster than the boiling point. Therefore, the vapor density does not fall, but, on the contrary, quickly increases with increasing boiling temperature.
Since the density of the liquid decreases and the density of the vapor increases, then, moving “up” along the boiling curve, we will inevitably reach a point at which the densities of the liquid and vapor are equal (Fig. 4.3).
At this remarkable point, which is called the critical point, the boiling curve ends. Since all the differences between gas and liquid are associated with the difference in density, at the critical point the properties of the liquid and gas become the same. Each substance has its own critical temperature and its own critical pressure. Thus, for water, the critical point corresponds to a temperature of 374 ° C and a pressure of 218.5 atm.
If you compress a gas whose temperature is below the critical temperature, then the process of its compression will be represented by an arrow crossing the boiling curve (Fig. 4.4). This means that at the moment of reaching a pressure equal to the vapor pressure (the point where the arrow intersects the boiling curve), the gas will begin to condense into a liquid. If our vessel were transparent, then at this moment we would see the beginning of the formation of a layer of liquid at the bottom of the vessel. At constant pressure, the layer of liquid will grow until finally all the gas turns into liquid. Further compression will require an increase in pressure.
The situation is completely different when compressing a gas whose temperature is above the critical one. The compression process can again be depicted as an arrow going from bottom to top. But now this arrow does not cross the boiling curve. This means that when compressed, the steam will not condense, but will only be continuously condensed.
At temperatures above the critical temperature, the existence of liquid and gas separated by an interface is impossible: When compressed to any density, there will be a homogeneous substance under the piston, and it is difficult to say when it can be called a gas and when a liquid.
The presence of a critical point shows that there is no fundamental difference between the liquid and gaseous states. At first glance, it might seem that there is no such fundamental difference only when we are talking about temperatures above critical. This, however, is not the case. The existence of a critical point indicates the possibility of turning a liquid - a real liquid that can be poured into a glass - into a gaseous state without any semblance of boiling.
This transformation path is shown in Fig. 4.4. A cross marks a known liquid. If you lower the pressure a little (down arrow), it will boil, and it will also boil if you raise the temperature a little (arrow to the right). But we will do something completely different. We will compress the liquid very strongly, to a pressure above critical. The point representing the state of the liquid will go vertically upward. Then we heat the liquid - this process is depicted by a horizontal line. Now, after we find ourselves to the right of the Critical Temperature, we lower the pressure to the original one. If you now reduce the temperature, you can get real steam, which could be obtained from this liquid in a simpler and shorter way.
Thus, it is always possible, by changing pressure and temperature bypassing the critical point, to obtain steam by continuously transferring it from liquid or liquid from steam. This continuous transition does not require boiling or condensation.
Early attempts to liquefy gases such as oxygen, nitrogen, and hydrogen were unsuccessful because the existence of a critical temperature was not known. These gases have very low critical temperatures: nitrogen -147°C, oxygen -119°C, hydrogen -240°C, or 33 K. The record holder is helium, its critical temperature is 4.3 K. Convert these gases into there is only one way to liquid - you need to reduce their temperature below the specified"
The similarity of the properties of unsaturated vapors and gases prompted M. Faraday to speculate: are gases not unsaturated vapors of the corresponding liquids? If the assumption is correct, then you can try to make them saturated and condense. Indeed, compression managed to make many gases saturated, except for six, which M. Faraday called “permanent”: nitrogen, hydrogen, air, helium, oxygen, carbon monoxide CO.
To understand what’s going on here, let’s study in more detail the isothermal process of compression (expansion) of steam. We have seen that the isotherm of a real gas differs from the isotherm of an ideal gas by the presence of a horizontal section corresponding to the region of existence of a two-phase system: saturated vapor and liquid.
If experiments are carried out at higher temperatures, then one can discover a pattern common to all substances (Fig. 1).
Firstly, the higher the temperature, the smaller the volume at which gas condensation begins: 
, If .
Secondly, the higher the temperature, the greater the volume occupied by the liquid after all the vapor has condensed:
Consequently, the length of the straight section of the isotherm decreases with increasing temperature.
This is easy to explain: with increasing T, the pressure of saturated steam increases rapidly, and in order for the pressure of unsaturated steam to equal the pressure of saturated steam, a decrease in volume is necessary. The reason for the increase in volume is the thermal expansion of the liquid when heated. Since the volume decreases, the vapor density increases with increasing temperature; an increase in volume indicates a decrease in the density of the liquid. This means that the difference between the liquid and its saturated vapor is smoothed out during such heating and at a sufficiently high temperature should disappear completely.
D. Mendeleev established that for each liquid there must be a temperature that was experimentally first established for many substances by T. Andrews and is called the critical temperature.
This is the temperature at which the density of the liquid and the density of its saturated vapor become the same (Fig. 2).
On isotherms at T = the horizontal section turns into an inflection point K.
The saturated vapor pressure of a substance at its critical temperature is called critical pressure. It is the highest possible saturated vapor pressure of a substance.
The volume occupied by a substance at and is called critical volume. This is the largest volume that the available mass of a substance in a liquid state can occupy.
At the critical temperature, the difference between gas and liquid disappears, and therefore the specific heat of vaporization becomes zero.
The set of points corresponding to the edges of the horizontal section of the isotherms (see Fig. 1) identifies in the p-V plane the regions of existence of a two-phase system and separates it from the regions of single-phase states of matter. The boundary curve of the region of two-phase states on the side of large volume values describes the state of saturated vapor and at the same time represents condensation curve(steam condensation begins during isothermal compression). The boundary curve on the side of smaller volumes is the curve on which condensation ends during compression of saturated vapor and evaporation of liquid begins during isothermal expansion. They call her evaporation curve.
The existence of a critical temperature of a substance explains why, at ordinary temperatures, some substances can be both liquid and gaseous, while others remain gases.
Above the critical temperature, liquid does not form even at very high pressures.
The reason is that here the intensity of the thermal motion of molecules turns out to be so great that even with their relatively dense packing caused by high pressure, molecular forces cannot ensure the creation of even short-range, much less long-range order.
Thus, it is clear that there is no fundamental difference between gas and steam. Typically, a gas is a substance in a gaseous state when its temperature is above a critical temperature. Steam is also called a substance in a gaseous state, but when its temperature is below critical. Steam can be converted into liquid only by increasing pressure, but gas cannot.
Currently, all gases are liquefied at very low temperatures. The last to be transferred was helium (= -269 °C) in 1908.
The similarity of the properties of unsaturated vapors and gases prompted M. Faraday to speculate: are gases not unsaturated vapors of the corresponding liquids? If the assumption is correct, then you can try to make them saturated and condense. Indeed, compression managed to make many gases saturated, except for six, which M. Faraday called “permanent”: nitrogen, hydrogen, air, helium, oxygen, carbon monoxide CO.
To understand what’s going on here, let’s study in more detail the isothermal process of compression (expansion) of steam. We have seen that the isotherm of a real gas differs from the isotherm of an ideal gas by the presence of a horizontal section corresponding to the region of existence of a two-phase system: saturated vapor and liquid.
If experiments are carried out at higher temperatures ( T 1 < T 2 < T 3 < T k< T 4), then one can detect a pattern common to all substances (Fig. 1).
Firstly, the higher the temperature, the smaller the volume at which gas condensation begins: V 1 > V' 1 > V'' 1 if T 1 < T 2 < T 3 .
Secondly, the higher the temperature, the greater the volume occupied by the liquid after all the vapor has condensed:
V 2 < V' 2 < V'' 2 .Consequently, the length of the straight section of the isotherm decreases with increasing temperature.
This is easy to explain: with growth Τ the pressure of saturated steam increases rapidly, and in order for the pressure of unsaturated steam to equal the pressure of saturated steam, a decrease in volume is necessary. Reason for the increase in volume V 2 - in the thermal expansion of the liquid when heated. Since the volume V 1 decreases, then the vapor density increases with increasing temperature; increase in volume V 2 indicates a decrease in liquid density. This means that the difference between the liquid and its saturated vapor is smoothed out during such heating and at a sufficiently high temperature should disappear completely.
D. Mendeleev established that for each liquid there must be a temperature that was experimentally first established for many substances by T. Andrews and is called the critical temperature.
Critical temperature T kr is the temperature at which the density of the liquid and the density of its saturated vapor become the same (Fig. 2).
On isotherms at T = T kr horizontal section turns into an inflection point TO.
The saturated vapor pressure of a substance at its critical temperature is called critical pressure p cr. It is the highest possible saturated vapor pressure of a substance.
The volume that a substance occupies when p cr and t kr, called critical volume m V cr. This is the largest volume that the available mass of a substance in a liquid state can occupy.
At the critical temperature, the difference between gas and liquid disappears, and therefore the specific heat of vaporization becomes zero.
A set of points corresponding to the edges of the horizontal section of isotherms (see Fig. 1) highlights in the plane p-V region of existence of a two-phase system and separates it from regions of single-phase states of matter. The boundary curve of the region of two-phase states on the side of large volume values describes the state of saturated vapor and at the same time represents condensation curve(steam condensation begins during isothermal compression). The boundary curve on the side of smaller volumes is the curve on which condensation ends during compression of saturated vapor and evaporation of liquid begins during isothermal expansion. They call her evaporation curve.
The existence of a critical temperature of a substance explains why, at ordinary temperatures, some substances can be both liquid and gaseous, while others remain gases.
Above the critical temperature, liquid does not form even at very high pressures.
The reason is that here the intensity of the thermal motion of molecules turns out to be so great that even with their relatively dense packing caused by high pressure, molecular forces cannot ensure the creation of even short-range, much less long-range order.
Thus, it is clear that there is no fundamental difference between gas and steam. Typically, a gas is a substance in a gaseous state when its temperature is above a critical temperature. Steam is also called a substance in a gaseous state, but when its temperature is below critical. Steam can be converted into liquid only by increasing pressure, but gas cannot.
Currently, all gases are liquefied at very low temperatures. The last to be transferred was helium in 1908 ( t cr = -269 °C).
Literature
Aksenovich L. A. Physics in secondary school: Theory. Tasks. Tests: Textbook. allowance for institutions providing general education. environment, education / L. A. Aksenovich, N. N. Rakina, K. S. Farino; Ed. K. S. Farino. - Mn.: Adukatsiya i vyakhavanne, 2004. - P. 176-178.
Tauride National University named after. IN AND. Vernadsky
Department of Experimental Physics
Laboratory work № 6
DEFINITION OF CRITICAL
TEMPERATURES OF SUBSTANCE
Simferopol 2002
DEFINITION OF CRITICAL
TEMPERATURES OF SUBSTANCE
EQUIPMENT : ampoule with ether, Avenarius device, autotransformer, thermocouple, galvanometer, calibration graph.
THEORETICAL PART OF THE WORK
AND 
A perfect gas is a collection of non-interacting material points. The state of such an idealized system is described by the Mendeleev-Clapeyron equation. In real gases, however, intermolecular forces of an electrical nature operate. When the distance between two molecules is small, repulsive forces act between them. These forces determine the “size” of gas molecules, that is, the distance closer to which the molecules strongly repel each other. As the distance between two molecules increases, the repulsion decreases and then changes its sign, turning into an attractive force. As the molecules move further away from each other, the attractive forces tend to zero. 
The interaction between molecules leads to the fact that real gases, at appropriate temperatures and pressures, transform into a liquid state.
On rice. 1 experimental isotherms obtained by compression of a real gas at a constant temperature T=const (T 1
Under certain conditions (gas without impurities, slow compression) it is possible to obtain the state c-d, called supersaturated steam . Under similar conditions of expansion of a liquefied gas, it is possible to obtain the state a-c, called superheated liquid . The states of supersaturated steam and superheated liquid are short-lived (metastable). From there, the system quickly returns to the site a-c.
As the temperature increases, the horizontal portion of the isotherms, corresponding to the condensation of saturated steam, decreases and at a certain temperature T cr(T 3 in Fig. 1) the transition region is compressed into one point TO. State of gas at a point TO called critical state of matter , and the corresponding values of temperature, pressure and volume are called critical. As the critical point is approached, the difference between the liquid and its saturated vapor disappears.
If T>T cr, then no compression of the gas transforms it into a liquid state.
Description of a device for observing the critical state of a substance and measuring critical temperature.
In this work, the critical temperature of a substance (ethyl ether) is determined by the disappearance and appearance of a visible liquid-vapor boundary. Sealed ampoule with ether 2 placed inside the heater 1 , the current for the heater is supplied from the network through an autotransformer. The temperature inside the heater is measured by a thermocouple 3 . There are glazed windows in the front and rear walls of the heater: the front for observation and the back for lighting. The heater is located inside a thick-walled casing with asbestos insulation. Thermo EMF is recorded with a millivoltmeter 4 . Graduation table 5 serves to convert thermo EMF into temperature.
COMPLETING OF THE WORK
Check that all parts of the installation are present. Ampoule from the heater don't take it out! Turn on the backlight. Connect the thermocouple to the galvanometer and apply current to the heater.
AFTER THE EXPERIMENT HAS BEEN STARTED, IT IS NOT PERMITTED TO OPEN THE CASING OR MAKE ANY CORRECTIONS INSIDE IT.
As it heats up, observe the readings of the galvanometer connected to the thermocouple circuit and use the calibration graph to judge the temperature inside the heater. Starting at 160˚С, observe the appearance of the meniscus in the ampoule.
Determine the temperature at which the meniscus disappears T 1 . Turn off the autotransformer. Observe the phenomena occurring in the ampoule. Determine temperature T 2 appearance of the meniscus. Calculate the average:
(1)
Perform the experiment three times. Calculate the error in determining the critical temperature.
CONTROL QUESTIONS
Describe the nature of intermolecular forces in a real gas.
Show on PV– a diagram of the isotherm of a real gas and interpret their character.
Show on PV-diagram and interpret the course of van der Waals gas isotherms.
How is the device designed to observe the critical state of a substance and measure the critical temperature?
Task. One of the models of a real gas proposed by Berthelot corresponds to the following equation of state:
where a, b are constants. Find Tcr, Pcr and Vcr for Berthelot gas, expressing these quantities in terms of constants a and b.
LITERATURE:
D.V.
Sivukhin. Thermodynamics and molecular physics.
