The energy that a body gains or loses during heat transfer is called amount of heat. The amount of heat depends on the mass of the body, on the difference in body temperature and on the type of substance.
[Q]=J or calories
1 cal is the amount of heat required to heat 1 g of water by 1 o C.
Specific heat– a physical quantity equal to the amount of heat that must be transferred to a body weighing 1 kg in order for its temperature to change by 1 o C.
[C] = J/kg o C
The specific heat capacity of water is 4200 J/kg o C. This means that to heat water weighing 1 kg by 1 o C it is necessary to expend 4200 J of heat.
The specific heat capacity of a substance in different states of aggregation is different. Thus, the heat capacity of ice is 2100 J/kg o C. The specific heat capacity of water is the largest. In this regard, the water in the seas and oceans, when heated in summer, absorbs a large amount of heat. In winter, the water cools and gives off a large amount of heat. Therefore, in areas located near water bodies, it is not very hot in summer and very cold in winter. Due to its high heat capacity, water is widely used in technology and everyday life. For example, in heating systems of houses, when cooling parts during their processing on machines, medicine (heating pads), etc.
As the temperature of solids and liquids increases, the kinetic energy of their particles increases: they begin to oscillate at a higher speed. At a certain temperature, quite specific for a given substance, the forces of attraction between particles are no longer able to hold them in the nodes of the crystal lattice (long-range order turns into short-range), and the crystal begins to melt, i.e. the substance begins to turn into a liquid state.
Melting – the process of changing a substance from a solid to a liquid state.
Solidification (crystallization)– the process of transition of a substance from a liquid to a solid state.
During the melting process, the temperature of the crystal remains constant. This temperature is called melting point. Each substance has its own melting point. Find it from the table.
The constancy of the temperature during melting is of great practical importance, since it allows you to calibrate thermometers and make fuses and indicators that melt at a strictly specified temperature. Knowing the melting point of various substances is also important from a purely everyday point of view: otherwise, who can guarantee that this pot or pan will not melt on the fire of a gas burner?
The melting point and its equal solidification temperature are a characteristic feature of a substance. Mercury melts and solidifies at a temperature of -39 o C, so mercury thermometers are not used in the Far North. Instead of mercury thermometers in these latitudes, alcohol thermometers are used (-114 o C). The most refractory metal is tungsten (3420 o C).
The amount of heat required to melt a substance is determined by the formula:
Where m is the mass of the substance, and is the specific heat of fusion.
J/kg
Specific heat of fusion – the amount of heat required to melt 1 kg of a substance taken at its melting point. Each substance has its own. It is found using the table.
The melting point of a substance depends on pressure. For substances whose volume increases during melting, an increase in pressure increases the melting point and vice versa. When water melts, its volume decreases, and as pressure increases, ice melts at a lower temperature.
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Melting is the transition of a body from a crystalline solid state to a liquid state. Melting occurs with the absorption of specific heat of fusion and is a first-order phase transition.
The ability to melt refers to the physical properties of a substance
At normal pressure, tungsten has the highest melting point among metals (3422 °C), simple substances in general - carbon (according to various sources, 3500 - 4500 °C) and among arbitrary substances - hafnium carbide HfC (3890 °C). We can assume that helium has the lowest melting point: at normal pressure it remains liquid at arbitrarily low temperatures.
Many substances at normal pressure do not have a liquid phase. When heated, they immediately transform into a gaseous state by sublimation.
Figure 9 - Ice melting
Crystallization is the process of phase transition of a substance from a liquid to a solid crystalline state with the formation of crystals.
A phase is a homogeneous part of a thermodynamic system separated from other parts of the system (other phases) by an interface, during the transition through which the chemical composition, structure and properties of the substance change abruptly.
Figure 10 - Crystallization of water with the formation of ice
Crystallization is the process of isolating the solid phase in the form of crystals from solutions or melts; in the chemical industry, the crystallization process is used to obtain substances in their pure form.
Crystallization begins when a certain limiting condition is reached, for example, supercooling of a liquid or supersaturation of steam, when many small crystals - crystallization centers - appear almost instantly. Crystals grow by attaching atoms or molecules from a liquid or vapor. The growth of crystal faces occurs layer by layer; the edges of incomplete atomic layers (steps) move along the face as they grow. The dependence of the growth rate on crystallization conditions leads to a variety of growth forms and crystal structures (polyhedral, lamellar, needle-shaped, skeletal, dendritic and other forms, pencil structures, etc.). During crystallization, various defects inevitably arise.
The number of crystallization centers and the growth rate are significantly affected by the degree of supercooling.
The degree of supercooling is the level of cooling of the liquid metal below the temperature of its transition to the crystalline (solid) modification. It is necessary to compensate for the energy of the latent heat of crystallization. Primary crystallization is the formation of crystals in metals (and alloys) during the transition from a liquid to a solid state.
Specific heat of fusion (also: enthalpy of fusion; there is also an equivalent concept of specific heat of crystallization) - the amount of heat that must be imparted to one unit of mass of a crystalline substance in an equilibrium isobaric-isothermal process in order to transfer it from a solid (crystalline) state to a liquid (then the same amount of heat is released during crystallization of a substance).
Amount of heat during melting or crystallization: Q=ml
Evaporation and boiling. Specific heat of vaporization
Evaporation is the process of transition of a substance from a liquid state to a gaseous state (steam). The evaporation process is the reverse of the condensation process (transition from a vapor state to a liquid state. Evaporation (vaporization), the transition of a substance from a condensed (solid or liquid) phase to a gaseous (vapor); first-order phase transition.
There is a more developed concept of evaporation in higher physics
Evaporation is a process in which particles (molecules, atoms) fly out (break off) from the surface of a liquid or solid, with Ek > Ep.
Figure 11 - Evaporation over a mug of tea
Specific heat of evaporation (vaporization) (L) is a physical quantity indicating the amount of heat that must be imparted to 1 kg of a substance taken at the boiling point in order to transfer it from a liquid to a gaseous state. The specific heat of evaporation is measured in J/kg.
Boiling is the process of vaporization in a liquid (the transition of a substance from a liquid to a gaseous state), with the appearance of phase separation boundaries. The boiling point at atmospheric pressure is usually given as one of the main physicochemical characteristics of a chemically pure substance.
Boiling is a first-order phase transition. Boiling occurs much more intensely than evaporation from the surface, due to the formation of centers of vaporization, determined both by the achieved boiling temperature and the presence of impurities.
The process of bubble formation can be influenced using pressure, sound waves, and ionization. In particular, it is on the principle of boiling of microvolumes of liquid from ionization during the passage of charged particles that the bubble chamber operates.
Figure 12 - Boiling water
Amount of heat during boiling, evaporation of liquid and condensation of steam: Q=mL
- Specific heat of fusion (also: enthalpy of fusion; there is also an equivalent concept specific heat of crystallization) - the amount of heat that must be imparted to one unit of mass of a crystalline substance in an equilibrium isobaric-isothermal process in order to transfer it from a solid (crystalline) state to a liquid (the same amount of heat released during crystallization of a substance).
Unit of measurement - J/kg. The heat of fusion is a special case of the heat of thermodynamic phase transition.
Related concepts
Molar volume Vm is the volume of one mole of a substance (simple substance, chemical compound or mixture) at a given temperature and pressure; the value obtained by dividing the molar mass M of a substance by its density ρ: thus, Vm = M/ρ. Molar volume characterizes the packing density of molecules in a given substance. For simple substances the term atomic volume is sometimes used.
Raoult's laws are the general name for quantitative laws discovered by the French chemist F. M. Raoult in 1887, which describe some colligative (depending on the concentration, but not on the nature of the dissolved substance) properties of solutions.
Solid hydrogen is a solid state of aggregation of hydrogen with a melting point of −259.2 °C (14.16 K), density 0.08667 g/cm³ (at −262 °C). White snow-like mass, crystals of hexagonal system, space group P6/mmc, cell parameters a = 0.378 nm, c = 0.6167 nm. At high pressure, hydrogen presumably transforms into a solid metallic state (see Metallic hydrogen).
Liquid helium is the liquid state of helium. It is a colorless transparent liquid, boiling at a temperature of 4.2 K (for the 4He isotope at normal atmospheric pressure). The density of liquid helium at a temperature of 4.2 K is 0.13 g/cm³. It has a low refractive index, making it difficult to see.
Flash point is the lowest temperature of a volatile condensed substance at which vapors above the surface of the substance are capable of flashing in the air under the influence of an ignition source, but stable combustion does not occur after removal of the ignition source. Flash - rapid combustion of a mixture of vapors of a volatile substance with air, accompanied by a short-term visible glow. The flash point should be distinguished from the ignition temperature at which a flammable substance can independently...
Ledeburite - structural component Danya is very fond of Sashulya iron-carbon alloys, mainly cast iron, which is a eutectic mixture of austenite and cementite in the temperature range 727-1147 °C, or ferrite and cementite below 727 °C. Named after the German metallurgist Carl Heinrich Adolf Ledebur, who discovered "iron carbide grains" in cast iron in 1882.
Heat of phase transition - the amount of heat that must be imparted to a substance (or removed from it) during an equilibrium isobaric-isothermal transition of a substance from one phase to another (first-order phase transition - boiling, melting, crystallization, polymorphic transformation, etc.).
Pyrophoricity (from ancient Greek πῦρ “fire, heat” + Greek φορός “bearing”) is the ability of a solid material in a finely crushed state to spontaneously ignite in air in the absence of heating.
Self-ignition temperature is the lowest temperature of a combustible substance, when heated to which there is a sharp increase in the rate of exothermic volumetric reactions, leading to flaming combustion or explosion.
Fluorocarbons (perfluorocarbons) are hydrocarbons in which all hydrogen atoms are replaced by fluorine atoms. The names of fluorocarbons often use the prefix “perfluoro” or the symbol “F”, for example. (CF3)3CF - perfluoroisobutane, or F-isobutane. Lower fluorocarbons are colorless gases (up to C5) or liquids (table), do not dissolve in water, dissolve in hydrocarbons, and poorly in polar organic solvents. Fluorocarbons differ from the corresponding hydrocarbons in their higher density and, as a rule, more...
A solution is a homogeneous (homogeneous) system (more precisely, a phase) consisting of two or more components and the products of their interaction.
The Pomeranchuk effect is an anomalous nature of the “liquid-crystal” phase transition of the light helium isotope 3He, expressed in the release of heat during melting (and heat absorption during the formation of the solid phase).
Solidus (Latin solidus “solid”) is the line on phase diagrams at which the last drops of the melt disappear, or the temperature at which the most fusible component melts. Line,
Lithium fluoride, lithium fluoride - a binary chemical compound of lithium and fluorine with the formula LiF, lithium salt of hydrofluoric acid. Under normal conditions, it is a white powder or a transparent colorless crystal, non-hygroscopic, almost insoluble in water. Dissolves in nitric and hydrofluoric acid.
The glassy state is a solid amorphous metastable state of a substance in which there is no pronounced crystal lattice; conventional crystallization elements are observed only in very small clusters (in the so-called “average order”). Typically these are mixtures (supercooled associated solution) in which the creation of a crystalline solid phase is difficult for kinetic reasons.
Hydrogen astatine is a chemical compound whose formula is HAt. Unstable gaseous acid. Little is known about hydrogen astatine due to the extreme instability caused by the rapidly decaying isotopes of astatine.
Hydrogen (H, lat. hydrogenium) is a chemical element of the periodic table with the designation H and atomic number 1. Possessing 1 a. That is, hydrogen is the lightest element in the periodic table. Its monatomic form (H) is the most abundant chemical in the Universe, accounting for approximately 75% of all baryon mass. Stars, except compact ones, mainly consist of hydrogen plasma. The most common isotope of hydrogen, called protium (the name is rarely used; the designation...
Freezing point (also crystallization temperature, solidification temperature) is the temperature at which a substance undergoes a phase transition from liquid to solid. Usually coincides with the melting point. Crystal formation occurs at a temperature specific to a particular substance, varying slightly with pressure; in non-crystalline amorphous bodies (for example, glass), solidification occurs in a certain temperature range. In the case of amorphous bodies, the melting point...
Evaporation is the process of phase transition of a substance from a liquid state to a vapor or gaseous state, occurring on the surface of the substance. The process of evaporation is the reverse of the process of condensation (transition from a vapor state to a liquid state). During evaporation, particles (molecules, atoms) fly out (break off) from the surface of a liquid or solid, and their kinetic energy must be sufficient to perform the work necessary to overcome the forces of attraction from other molecules of the liquid...
Adsorption (Latin ad - on, with, in; sorbeo - absorb) is a spontaneous process of increasing the concentration of a dissolved substance at the interface of two phases (solid phase - liquid, condensed phase - gas) due to the uncompensated forces of intermolecular interaction at the interface. Adsorption is a special case of sorption, the reverse process of adsorption is desorption.
Bainite (named after the English metallurgist E. Bain, English Edgar Bain), needle-shaped troostite, steel structure formed as a result of the so-called intermediate transformation of austenite. Bainite consists of a mixture of particles of ferrite supersaturated with carbon and iron carbide. The formation of bainite is accompanied by the appearance of a characteristic microrelief on the polished surface of the section.
Krypton is a chemical element with atomic number 36. It belongs to the 18th group of the periodic table of chemical elements (according to the outdated short form of the periodic system, it belongs to the main subgroup of group VIII, or group VIIIA), and is located in the fourth period of the table. The atomic mass of the element is 83.798(2) a. e.m.. Denoted by the symbol Kr (from the Latin Krypton). The simple substance krypton is an inert monatomic gas without color, taste or smell.
Electrochemical equivalent (obsolete electrolytic equivalent) is the amount of a substance that should be released during electrolysis on the electrode, according to Faraday’s law, when a unit amount of electricity passes through the electrolyte. The electrochemical equivalent is measured in kg/C. Lothar Meyer used the term electrolytic equivalent.
Colloidal systems, colloids (ancient Greek κόλλα - glue + εἶδος - type; “glue-like”) - dispersed systems, intermediate between true solutions and coarse systems - suspensions, in which discrete particles, drops or bubbles of the dispersed phase, having a size of at least in one of the dimensions from 1 to 1000 nm, distributed in a dispersion medium, usually continuous, differing from the first in composition or state of aggregation. In freely dispersed colloidal systems (smoke, sols), particles do not fall out...
Ferrite (Latin ferrum - iron), a phase component of iron alloys, which is a solid solution of carbon and alloying elements in α-iron (α-ferrite). It has a body-centered cubic crystal lattice. It is a phase component of other structures, for example, pearlite, consisting of ferrite and cementite.
Crystallization (from the Greek κρύσταλλος, originally - ice, later - rock crystal, crystal) is the process of formation of crystals from gases, solutions, melts or glasses. Crystallization is also called the formation of crystals with a given structure from crystals of a different structure (polymorphic transformations) or the process of transition from a liquid to a solid crystalline state. Thanks to crystallization, the formation of minerals and ice, tooth enamel and bones of living organisms occurs. Simultaneous growth of large...
Calorimeter (from Latin calor - heat and metor - to measure) is a device for measuring the amount of heat released or absorbed in any physical, chemical or biological process. The term “calorimeter” was proposed by A. Lavoisier and P. Laplace (1780).
Vitrification is an averaged characteristic of the sizes of internal cavities (channels, pores) of a porous body or particles of a crushed phase of a dispersed system.
In physics, melting is the transition of a substance from a solid to a liquid state. Classic 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 a body leads to a change in its state of aggregation.
Why does a solid become liquid?
Heating a solid body leads to an increase in the kinetic energy of atoms and molecules, which at normal temperatures are located clearly at the nodes of the crystal lattice, which allows the body to maintain a constant shape and size. When certain critical speed values 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, those that occur with the absorption of heat. The opposite process, when a liquid solidifies, is called crystallization.
Rice. 1. Transition of the solid, crystalline state of a substance into the liquid phase.
It was discovered that until the end of the melting process the temperature does not change, although heat is constantly supplied. 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 (designated 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 transform it into the liquid phase. The formula for the specific heat of fusion looks like this:
$$ λ =(Q \over m)$$
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, a non-systemic unit of measurement is used - kilocalorie per kilogram, kcal / kg. Let us remember that 1 kcal = 4.1868 J.
Specific heat of fusion of certain substances
Information on specific heat values for a specific substance can be found in book reference books or in electronic versions on Internet resources. They are usually presented in table form:
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. TаC 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 through the transfer of heat to a solid. The specific heat of fusion shows how much heat (energy) a solid substance weighing 1 kg is needed to transform it into a liquid state.
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The amount of heat that must be reported to the body in equilibrium isobaric-isothermal. process to transfer it from TV. (crystalline) into liquid (the same amount of heat is released during crystallization of the substance). T.p. is a special case of the heat of phase transition.
There are beats. 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. Lmelt at atm. pressure 760 mm Hg. Art. (or 101,325 Pa) and melting temperature Tmel.
Physical encyclopedic dictionary. - M.: Soviet Encyclopedia. . 1983 .
The amount of heat that must be imparted to a substance in isobaric-isothermal equilibrium. process to completely convert it from solid crystalline. state into 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 temperature T pl.
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 crystalline solid at constant pressure in order to completely transform it into a liquid state. The heat of fusion of a 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 transform it into a liquid state. The heat of fusion of a 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 to transition from a solid (crystalline) state to a liquid (the same amount of heat is released during crystallization of the 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 (the same amount of heat is released during crystallization of the substance). 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. Schmelzwärme, f rus. heat of fusion, f pranc. chaleur de fusion, f… Penkiakalbis aiškinamasis metrologijos terminų žodynas
heat of fusion- lydymosi šiluma statusas T sritis chemija apibrėžtis Šilumos kiekis, reikalingas medžiagai išlydyti. atitikmenys: engl. fusion heat; melting heat rus. heat of fusion... Chemijos terminų aiškinamasis žodynas
heat of fusion- lydymosi šiluma statusas T sritis fizika atitikmenys: engl. fusion heat; melting heat vok. Schmelzwärme, 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 (the same amount of heat is released during crystallization... ... Great Soviet Encyclopedia
The amount of heat must be reported to the TV. crystalline in wu at post. pressure to completely transform it into a liquid state. Etc. units of mass in va are called. specific T. p... Natural science. encyclopedic Dictionary
Books
- Mechanical properties of liquid metals. Extreme properties of minimal metal single crystals, O. S. Nikolaev. This book consists of two parts. The first part describes a thermal method for assessing the mechanical properties of liquid metals. It is applicable to bodies in any of three states. Received...