The amount of heat, which must be reported in-woo in an equilibrium isobaric-isothermal. process to translate it from TV. (crystal) into liquid (the same amount of heat is released during the crystallization of the island). T. p. is a special case of the heat of a phase transition.

Distinguish ud. T. p. (measured in J / kg, kcal / kg) and molar (molar) T. p. (J / mol). In table. the values ​​of beats are given. T. p. Lpl at atm. pressure 760 mm Hg. Art. (or 101 325 Pa) and melting temperature Tm.

Physical Encyclopedic Dictionary. - M.: Soviet Encyclopedia. . 1983 .

The amount of heat, which must be reported to the substance in an equilibrium isobaric-isothermal. process to completely transfer it from a solid crystalline. state to liquid. T. p. is equal to the amount of heat released during the crystallization of a substance from the liquid phase. T. L pl for certain substances at normal pressure (1013.25 hPa) and melting point T sq.

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

See what "HEAT OF MELTING" is in other dictionaries:

The amount of heat that must be imparted to a solid crystalline substance at constant pressure in order to completely convert it into a liquid state. The heat of fusion per unit mass of a substance is called the specific heat of fusion. * * *… … encyclopedic Dictionary

The amount of heat that must be imparted to a solid crystalline substance at constant pressure in order to completely convert it into a liquid state. The heat of fusion per unit mass of a substance is called the specific heat of fusion... Big Encyclopedic Dictionary

heat of fusion- the amount of heat required by a substance in an equilibrium isobaric isothermal process for the transition from a solid (crystalline) state to a liquid state (the same amount of heat is released during the crystallization of a substance). Warmth… … Encyclopedic Dictionary of Metallurgy

The amount of heat that must be imparted to a substance in an equilibrium process in order to transfer it from a solid (crystalline) state to a liquid state (the same amount of heat is released during the crystallization of a substance). The heat of fusion ... ... Metallurgical Dictionary

heat of fusion- lydymosi šiluma statusas T sritis Standartizacija ir metrologija apibrėžtis Šilumos kiekis, reikalingas medžiagai išlydyti. atitikmenys: engl. fusion heat; melting heat vok. Schmelzwarme, f rus. heat of fusion, f pranc. chaleur de fusion, f … Penkiakalbis aiskinamasis metrologijos terminų žodynas

heat of fusion- lydymosi šiluma statusas T sritis chemija apibrėžtis Šilumos kiekis, reikalingas medžiagai išlydyti. atitikmenys: engl. fusion heat; melting heat. melting heat... Chemijos terminų aiskinamasis žodynas

heat of fusion- lydymosi šiluma statusas T sritis fizika atitikmenys: engl. fusion heat; melting heat vok. Schmelzwarme, f rus. heat of fusion, f pranc. chaleur de fusion, f … Fizikos terminų žodynas

heat of fusion- lydymosi šiluma statusas T sritis Energetika apibrėžtis Šiluma, reikalinga kietai kristalinei medžiagai paversti skysčiu, esant pastoviai lydymosi temperatūrai. Būna savitoji ir molinė lydymosi šiluma. Jų matavimo vienetai - džaulis kilogramui ... ... Aiškinamasis šiluminės ir branduolinės technikos terminų žodynas

The amount of heat that must be imparted to a substance in an equilibrium isobaric isothermal process in order to transfer it from a solid (crystalline) state to a liquid one (the same amount of heat is released during crystallization ... ... Great Soviet Encyclopedia

Number of heat, to the swarm it is necessary to report TV. crystalline in wu at post. pressure to completely convert it into a liquid state. T. p. units of mass in vaz. specific T. p ... Natural science. encyclopedic Dictionary

Books

• Mechanical properties of liquid metals. Extreme properties of minimal single crystals of metals, O. S. Nikolaev. This book consists of two parts. The first part describes the thermal method for assessing the mechanical properties of liquid metals. It is applicable to bodies in any of the three states. Received…

In physics, melting is the transition of a substance from a solid to a liquid state. Classical examples of the melting process are the melting of ice and the transformation of a solid piece of tin into liquid solder when heated with a soldering iron. The transfer of a certain amount of heat to the body leads to a change in its state of aggregation.

Why does solid become liquid?

Heating a solid body leads to an increase in the kinetic energy of atoms and molecules, which at normal temperature are clearly located at the nodes of the crystal lattice, which allows the body to maintain a constant shape and size. When certain critical speeds are reached, atoms and molecules begin to leave their places, bonds are broken, the body begins to lose its shape - it becomes liquid. The melting process does not occur abruptly, but gradually, so that for some time the solid and liquid components (phases) are in equilibrium. Melting refers to endothermic processes, that is, to those that occur with the absorption of heat. The opposite process, when a liquid solidifies, is called crystallization.

Rice. 1. The transition of a solid, crystalline, state of matter into a liquid phase.

It was found that until the end of the melting process, the temperature does not change, although heat is supplied all the time. There is no contradiction here, since the incoming energy during this period of time is spent on breaking the crystalline bonds of the lattice. After the destruction of all bonds, the influx of heat will increase the kinetic energy of the molecules, and, consequently, the temperature will begin to rise.

Rice. 2. Graph of body temperature versus heating time.

Determination of specific heat of fusion

The specific heat of fusion (denoted by the Greek letter “lambda” - λ) is a physical quantity equal to the amount of heat (in joules) that must be transferred to a solid body weighing 1 kg in order to completely transfer it to the liquid phase. The formula for the specific heat of fusion is:

$$ λ =(Q \over m)$$

m is the mass of the melting substance;

Q is the amount of heat transferred to the substance during melting.

Values ​​for different substances are determined experimentally.

Knowing λ, we can calculate the amount of heat that must be imparted to a body of mass m for its complete melting:

In what units is the specific heat of fusion measured?

Specific heat of fusion in SI (International System) is measured in joules per kilogram, J / kg. For some tasks, an off-system unit of measurement is used - kilocalorie per kilogram, kcal / kg. Recall that 1 kcal = 4.1868 J.

Specific heat of fusion of some substances

Information on specific heat values ​​for a particular substance can be found in book references or in electronic versions on Internet resources. They are usually presented in the form of a table:

Specific heat of fusion of substances

One of the most refractory substances is tantalum carbide - TaC. It melts at a temperature of 3990 0 C. TaC coatings are used to protect metal molds in which aluminum parts are cast.

Rice. 3. Metal melting process.

What have we learned?

We learned that the transition from solid to liquid is called melting. Melting occurs by transferring heat to a solid. The specific heat of fusion shows how much heat (energy) is needed for a solid substance weighing 1 kg to convert it into a liquid state.

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Density, thermal conductivity and heat capacity of ice depending on temperature

The table shows the values ​​of density, thermal conductivity, specific heat capacity of ice depending on the temperature in the range from 0 to -100°C.

According to the table, it can be seen that with decreasing temperature, the specific heat capacity of ice decreases, while the thermal conductivity and density of ice, on the contrary, increase. For example, at a temperature of 0 ° C, the density of ice has a value of 916.2 kg / m 3, and at a temperature of minus 100°C, its density becomes equal to 925.7 kg/m 3 .

The specific heat capacity of ice at 0°C is 2050 J/(kg deg). When the temperature of ice decreases from -5 to -100°C, its specific heat capacity decreases by 1.45 times. The heat capacity of ice is two times less.

The thermal conductivity of ice when its temperature is lowered from 0 to minus 100°C increases from 2.22 to 3.48 W/(m deg). Ice is more thermally conductive than water - it can conduct 4 times more heat under the same boundary conditions.

It should be noted that the density of ice is less, however, with decreasing temperature, the density of ice increases and, as the temperature approaches absolute zero, the density of ice becomes close to the density of water.

Thermophysical properties of ice and snow

The table shows the following properties of ice and snow:

• ice density, kg/m 3 ;
• thermal conductivity of ice and snow, kcal/(m h deg) and W/(m deg);
• specific mass heat capacity of ice, kcal/(kg deg) and J/kg deg);
• thermal diffusivity, m 2 /hour and m 2 /sec.

The properties of ice and snow are presented depending on the temperature in the range: for ice from 0 to -120°C; for snow from 0 to -50°С depending on compaction (density). The thermal diffusivity of ice and snow in the table is given with a factor of 10 6 . For example, the thermal diffusivity of ice at 0°C is 1.08·10 -6 m 2 /s.

Saturated vapor pressure of ice

The table shows the pressure values ​​of the saturated steam of ice during sublimation (transition of ice into vapor, past the liquid phase) depending on the temperature in the range from 0.01 to -80°C. It can be seen from the table that as the temperature of the ice decreases, the pressure of its saturated vapor decreases.

Sources:

1. Volkov. A.I., Zharsky. THEM. Big chemical reference book. - M: Soviet School, 2005. - 608 p.

The processes of crystallization and melting describe the same physical quantities. The difference is that during melting, the body needs energy to destroy the lattice, and during crystallization, on the contrary, the body gives off energy to the environment.

The concept of specific heat of crystallization

The specific heat of crystallization (melting) is understood as the amount of energy released (consumed) by 1 kg. substances during the transition from a liquid to a solid state (and vice versa). It is important to note that in the process of crystallization (melting) the temperature of the substance does not change and it has already been brought to a value at which the process itself is possible.

The specific heat of crystallization (melting) is measured in J / kg., It is denoted by the letter of the Greek alphabet λ. A-priory:

where Q is the amount of energy released (consumed) by m kilograms of matter.

Calculation of energy in sequential thermal processes

Consider the process of cooling m kg of water from a temperature, for example, +20°C to -10°C. Here we are dealing with three thermal processes:

• water cooling from +20°С to 0°С, ∆T1 = - 20°;
• crystallization of water into ice at 0°C;
• ice cooling from 0°С to -10°С, ∆T2 = - 10°;

The amount of released energy Q is equal to the sum of the energies in each of these processes:

Q = Q1 + Q2 + Q3;

Q1 = C1 * m * ∆T1;

Q3 = C2 * m * ∆T2;

where C1 and C2 are the specific heat capacities of water and ice, respectively. The “-” sign at Q2 means that the process of energy release during crystallization is underway.