Thermodynamic temperature scale. Thermodynamic temperature What is a thermodynamic scale

Temperature that does not depend on the properties of the thermometric substance (the reference point is absolute zero temperature). The construction of a thermodynamic temperature scale is based on the second law of thermodynamics and, in particular, on the independence of efficiency Carnot cycle from the nature of the working fluid. The unit of thermodynamic temperature, the kelvin (K), is defined as 1/273.16 of the thermodynamic temperature of the triple point of water.

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See Art. Temperature scale. Physical encyclopedia. In 5 volumes. M.: Soviet encyclopedia. Editor-in-Chief A. M. Prokhorov. 1988 ... Physical encyclopedia

- (see TEMPERATURE SCALES). Physical encyclopedic dictionary. M.: Soviet Encyclopedia. Editor-in-chief A. M. Prokhorov. 1983 ... Physical encyclopedia

- (Kelvin scale), absolute temperature scale, independent of the properties of the thermometric substance (reference point absolute zero temperature). The construction of a thermodynamic temperature scale is based on the second law of thermodynamics and, in... ... Encyclopedic Dictionary

thermodynamic temperature scale- termodinaminė temperatūros skalė statusas T sritis Standartizacija ir metrologija apibrėžtis Temperatūros skalė, pagrįsta absoliučiuoju nuliu, t. y. žemiausia temperatūra, kurią teoriškai galima būtų pasiekti ir kuri yra 273.16 °C žemiau ledo… … Penkiakalbis aiškinamasis metrologijos terminų žodynas

thermodynamic temperature scale- termodinaminė temperatūros skalė statusas T sritis Energetika apibrėžtis Nepriklauso nuo termometrinės medžiagos ir turi vieną atskaitos tašką – vandens trigubąjį tašką, kuriam suteikta T = 273.16 K vertė. Termodinaminė temperatūros skalė… … Aiškinamasis šiluminės ir branduolinės technikos terminų žodynas

- (Kelvin scale), abs. temperature scale p, independent of thermometric properties. in va (absolute zero temperature reference point). Construction of T. t. sh. based on the second law of thermodynamics and, in particular, on the independence of the efficiency of the Carnot cycle from the nature of the working... ... Natural science. Encyclopedic Dictionary

See Temperature Scales... Great Soviet Encyclopedia

Kelvin temperature scale - Thermodynamic scale temperature (TK), in which 0°K=–273.16°C (1K=1°C). Syn.: absolute temperature scale; Kelvin scale... Dictionary of Geography

TEMPERATURE SCALE- a series of numerical points on the thermometer scale, distributed within a temperature interval limited by two points of constant temperature, taken as the main main reference points (usually for the same physical states, for example temperature ... ... Big Polytechnic Encyclopedia

Chaotic thermal movement on the plane of gas particles such as atoms and molecules There are two definitions of temperature. One with molecular kinetic point vision, another with thermodynamics. Temperature (from Latin temperatura proper ... ... Wikipedia

See Art. Temperature scale.

Physical encyclopedia. In 5 volumes. - M.: Soviet Encyclopedia. Editor-in-chief A. M. Prokhorov. 1988 .

See what "THERMODYNAMIC TEMPERATURE SCALE" is in other dictionaries:

- (Kelvin scale) is an absolute temperature scale that does not depend on the properties of the thermometric substance (the reference point is absolute zero temperature). The construction of a thermodynamic temperature scale is based on the second law of thermodynamics and, in particular... Big Encyclopedic Dictionary

- (see TEMPERATURE SCALES). Physical encyclopedic dictionary. M.: Soviet Encyclopedia. Editor-in-chief A. M. Prokhorov. 1983 ... Physical encyclopedia

- (Kelvin scale), an absolute temperature scale that does not depend on the properties of the thermometric substance (the reference point is absolute zero temperature). The construction of a thermodynamic temperature scale is based on the second law of thermodynamics and, in... ... Encyclopedic Dictionary

See Temperature Scales... Great Soviet Encyclopedia

Kelvin temperature scale- Thermodynamic temperature scale (TC), in which 0°K=–273.16°C (1K=1°C). Syn.: absolute temperature scale; Kelvin scale... Dictionary of Geography

Chaotic thermal motion on a plane of gas particles such as atoms and molecules There are two definitions of temperature. One from a molecular kinetic point of view, the other from a thermodynamic point of view. Temperature (from Latin temperatura proper ... ... Wikipedia

Let us remember that in practice, 0° is conventionally taken to be the melting temperature of ice at normal pressure, and 100° is the boiling temperature of water at normal pressure. One hundredth of this temperature range is the practical unit of temperature, degrees Celsius (°C). However, when dividing the interval between 0 °C and 100 °C by one hundred equal parts For mercury and alcohol thermometers, their readings coincide only at 0 °C and at 100 °C. Consequently, the expansion of these substances when heated occurs unevenly and it is impossible to obtain a single temperature scale in this way.

To create a unified temperature scale, you need to have a value whose measurement during heating or cooling would not depend on the type of thermometric substance. This value can be gas pressure, since temperature coefficient pressure for not too dense gases does not depend on the nature of the gas and has the same meaning as for ideal gas. The best thermometric body would be an ideal gas. Since the properties of rarefied hydrogen are closest to the properties of an ideal gas, it is most advisable to measure the temperature using a hydrogen thermometer, which is a closed vessel with rarefied hydrogen connected to a sensitive pressure gauge. Since the pressure and temperature of hydrogen are related by relation (4.3), the temperature can be determined from the pressure gauge reading.

The temperature scale established by a hydrogen thermometer, in which 0° corresponds to the melting temperature of ice, and 100° to the boiling temperature of water, is called the Celsius scale.

Note that zero on the Celsius scale is defined conditionally. The size of the degree is also determined arbitrarily. This means that with scientific point From a different point of view, a different construction of the temperature scale is permissible.

The appropriate choice of temperature scale allows you to simplify formulas and gain a deeper understanding physical meaning observed patterns. For this purpose, at the suggestion of Kelvin, a new temperature scale was introduced, which is now called the thermodynamic temperature scale. It is sometimes called the Kelvin scale. On this scale, the temperature of absolute zero is taken as the starting point, and the size of the degree is determined so that it coincides as closely as possible with the degree Celsius.

In SI, the unit of temperature is the basic one and is called the kelvin, and the thermodynamic temperature scale is used to measure temperature.

By international agreement, the size of the kelvin is determined from the following condition: the temperature of the triple point of water (§ 12.8) is considered to be exactly equal to 273.16 K. Therefore, if the temperature interval between absolute zero and the triple point temperature of water on the scale of a hydrogen thermometer is divided into 273.16 parts, then one such part determines the size of the kelvin. Since the triple point of water corresponds to temperature, the melting temperature of ice on the new scale will be 273.15 K. Since a kelvin is equal in value to a degree Celsius, the boiling point of water at normal pressure will be 373.15 K. To simplify the melting and boiling temperatures of ice in the future water will accordingly be considered equal to 273 and 373 K.

In ch. I, considering methods for measuring temperature, we noted that such measurements pose serious difficulties. It lies in the fact that the temperature scales established using various thermometric bodies do not coincide with each other.

Now, however, we have become acquainted with one property which is completely independent of the type of substance and which can therefore serve as an impeccable thermometric property for establishing a temperature scale. This property consists in the fact that any substance, if used as a working fluid in a reversible heat engine, gives the same efficiency (of course, at the same temperatures of the heater and refrigerator).

If the working fluid, whatever it may be, absorbs heat at temperature and transfers heat to the refrigerator at temperature, then the following relation is true:

The last relationship, valid for any substance, allows the Carnot machine to be used as a kind of thermometer. True, this “thermometer” allows you to determine only the ratio of two temperatures and not the temperatures themselves. But if we agree to assign a certain numerical value to one of these temperatures or select it in one way or another

the size of the degree, then the desired temperature will be determined.

In this way, a temperature scale will be established that does not depend on the type of substance, that is, a scale that is physically flawless.

Let us explain with an example how to measure temperature with such an unusual “thermometer”. Suppose we need to measure the temperature of a certain body, and we have no thermometers at our disposal except a Carnot machine.

Let us take as a heater in a Carnot machine a heat reservoir at the boiling temperature of water (we, of course, will not measure this temperature, since we do not have a thermometer for this purpose), and as a refrigerator, a heat reservoir at the temperature of melting ice (which we for the same reason we will not measure either). Let us also agree that we will divide the temperature difference between the heater and the refrigerator into 100 parts (degrees); we could have chosen any other number, just like we could have chosen any other heat reservoirs. In addition to the Carnot machine, we also need a calorimeter to measure quantities of heat. After all, in the Carnot “thermometer” the thermometric problem turns into a calorimetric one.

Let us now carry out a reversible Carnot cycle between the heater and refrigerator we have chosen, using any working fluid (after all, nothing depends on it), and measure the amount of heat Fiagr. received from the heater, and the amount of heat given to the refrigerator. Let us denote by and the temperatures (still unknown) of boiling water, melting ice and the body under study. Then we can write:

Then we will carry out the Carnot cycle again, but with the body under study as a refrigerator and with the same heater, or, conversely, with the same refrigerator, but with the body under study as a heater. Having again measured the heat received from the heater, which will remain the same as in the first experiment, and the heat given to the refrigerator, we can again write the relation

We thus have two equations (92.2) and (92.3) to determine the three quantities and But we can,

in addition, write the third equation that determines the size of the degree:

These three equations are sufficient to determine the desired temperature and the values of Theat and Tcol.

It remains to add that we could run our heat engine in the opposite direction, so that it would work like a refrigeration machine. Then we would have to measure the amount of heat transferred from the refrigerator to the heater, and the magnitude external work spent on this.

Of course, no one has ever measured temperature in such an unusual way, which is also technically impossible. But there is no need for this, because the temperature scale established using the Carnot machine can be reproduced using any specific substance with well-known properties. Such a substance is, for example, an ideal gas, for which the equation of state is precisely known. As was shown, formula (92.1) is obtained if an ideal gas is used as a working fluid in a Carnot machine. It can be shown that temperatures measured on the scale of a gas thermometer, where the temperature is obtained from the formula

exactly the same as the temperature that would have been obtained if the experiment described above had been carried out.

Note that a temperature scale based on the properties of a reversible Carnot machine is called a thermodynamic temperature scale. It was proposed by Kelvin and therefore temperatures expressed in this scale are measured in Kelvin.

As for the zero of the thermodynamic scale, it is clear from formula (80.12) that the zero should be the temperature at which In this case, the efficiency of the Carnot machine is equal to unity, and, therefore, there cannot be a lower temperature, since k. . p.d. cannot exceed one.

Since the thermodynamic temperature scale coincides with the scale of an ideal gas, the zero of the Kelvin scale coincides with the absolute zero of temperature, which we defined earlier. It should be noted, however, that according to the second law of thermodynamics, the efficiency of a heat engine can never be equal to unity: the amount of heat received from the heater cannot be completely converted into mechanical work. Therefore, absolute zero temperature cannot be reached.

Carnot's theorem allows us to construct a temperature scale that is completely independent of individual characteristics thermometric substance and thermometer device. This temperature scale was proposed by W. Thomson (Lord Kelvin) in 1848. It is constructed as follows. Let t 1 and t 2 heater and refrigerator temperatures measured with some kind of thermometer. Then, according to Carnot’s theorem, the efficiency of the Carnot cycle

Where f(t 1 ,t 2) – universal function of selected empirical temperatures t 1 and t 2. Its appearance is completely independent of the specific design of the Carnot machine and the type of working substance used. In the future, it will be more convenient for us to consider a simpler universal temperature function

This function is easily expressed through f(t 1 ,t 2). To determine general view functions j( t 1 ,t 2), consider three thermal reservoirs whose temperatures are maintained constant. We denote the empirical temperatures of these reservoirs t 1 , t 2 , t 3 respectively. Using them as heaters and refrigerators, we will perform three Carnot cycles ( a-b-c-d, d-c-e-f, a-b-e-f) shown in Fig. 11.1.

At the same time, the temperatures on the isotherms a-b, d-c, f-e equal t 1 , t 2 , t 3, and the absolute values of the heats obtained on the isotherms are equal Q 1 , Q 2 , Q 3 respectively. For cycles a-b-c-d And d-c-e-f you can write

Excluding from here Q 2, we get

Combined together, these two cycles are equivalent to one Carnot cycle a-b-e-f, because isotherm c-d is traversed twice in opposite directions and can be excluded from consideration. Hence,

Comparing this expression with the previous one, we get

Since the right side does not depend on t 2, then this relation can be satisfied for any values of the arguments t 1 , t 2 , t 3 only if function j( t 1 ,t 2) has the form

Thus j( t 1 ,t 2) is the ratio of values of the same function Q( t) at t = t 1 and t = t 2. Since the quantity Q( t) depends only on temperature; it itself can be taken as a measure of body temperature. The quantity Q is called the absolute thermodynamic temperature. The ratio of two thermodynamic temperatures Q 1 and Q 2 is determined by the relation

Then the efficiency of the Carnot cycle can be written as

. (11.2)

Comparing expression (11.2) with the efficiency of the Carnot cycle for an ideal gas (8.2), one can verify that the ratios of the thermodynamic and ideal gas temperatures of thermal reservoirs in the Carnot cycle coincide.

The ratio Q 1 /Q 2 can, in principle, be found experimentally. To do this, you need to measure the absolute values of heat Q 1 and Q 2, which the working fluid receives in the Carnot cycle from thermal reservoirs with temperatures Q 1 and Q 2. However, the temperatures Q 1 and Q 2 themselves are not yet uniquely determined by the value of this ratio.

To unambiguously determine the absolute thermodynamic temperature, one should assign a certain value Q to any temperature point, and then use relation (11.1) to calculate the temperature of any other body. Based on the accuracy with which it is possible to reproduce certain characteristic temperatures, the triple point of water was chosen as the main reference point, i.e. temperature at which ice, water and water vapor are in equilibrium (pressure at the same time R tr = 4.58 mm. Hg Art.). This temperature is assigned the value T tr = 273.16 K exactly. This value of the reference temperature was chosen in order to ensure the coincidence of the thermodynamic temperature with the ideal gas temperature within the limits of applicability of the latter.

The constructed temperature scale is called the absolute thermodynamic temperature scale (Kelvin scale).

The Carnot machine allows one to construct a temperature scale only in principle. It is unsuitable for practical temperature measurements. However, numerous consequences of the second law of thermodynamics and Carnot's theorem make it possible to find corrections to the readings of real thermometers, bringing these readings to the absolute thermodynamic scale. For this purpose, you can use any precise thermodynamic relationship, which in addition to temperature T only experimentally measurable quantities are included.