In physics, heat, symbolized by Q, is energy transferred from one body or system to another due to a difference in temperature. Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός In Thermodynamics, a thermodynamic system, originally called a working substance, is defined as that part of the universe that is under consideration Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature [1][2] In thermodynamics, the quantity TdS is used as a representative measure of heat, which is the absolute temperature of an object multiplied by the differential quantity of a system's entropy measured at the boundary of the object. In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " Thermodynamic temperature is the absolute measure of Temperature and is one of the principal parameters of Thermodynamics. In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy In Thermodynamics, a boundary is a real or imaginary volumetric demarcation region drawn around a Thermodynamic system across which quantities such as Heat Heat can flow spontaneously from an object with a high temperature to an object with a lower temperature. The transfer of heat from one object to another object with an equal or higher temperature can happen only with the aid of a heat pump. A heat pump is a machine or device that moves Heat from one location (the 'source' to another location (the 'sink' or 'heat sink' using work. High temperature bodies, which often result in high rates of heat transfer, can be created by chemical reactions (such as burning), nuclear reactions (such as fusion taking place inside the Sun), electromagnetic dissipation (as in electric stoves), or mechanical dissipation (such as friction). In thermal physics, heat transfer is the passage of Thermal energy from a hot to a colder body A chemical reaction is a process that always results in the interconversion of Chemical substances The substance or substances initially involved in a chemical reaction are called Combustion or burning is a complex sequence of Exothermic chemical reactions between a Fuel and an Oxidant accompanied by the production of In Nuclear physics, a nuclear reaction is the process in which two nuclei or nuclear particles collide to produce products different from the initial particles In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus The Sun (Sol is the Star at the center of the Solar System. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. In Physics, dissipation embodies the concept of a Dynamical system where important mechanical modes such as Waves or Oscillations lose Energy In Cooking, an electric stove is a Cooker which uses Electricity as a source of Energy. Mechanics ( Greek) is the branch of Physics concerned with the behaviour of physical bodies when subjected to Forces or displacements Friction is the Force resisting the relative motion of two Surfaces in contact or a surface in contact with a fluid (e Heat can be transferred between objects by radiation, conduction and convection. Thermal radiation is Electromagnetic radiation emitted from the surface of an object which is due to the object's Temperature. Heat conduction or thermal conduction is the spontaneous transfer of thermal energy through matter from a region of higher Temperature to a region of lower Convection in the most general terms refers to the movement of molecules within Fluids (i Temperature is used as a measure of the internal energy or enthalpy, that is the level of elementary motion giving rise to heat transfer. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature In Thermodynamics and molecular chemistry, the enthalpy (denoted as H, h, or rarely as χ) is a quotient or description of Heat can only be transferred between objects, or areas within an object, with different temperatures (as given by the zeroth law of thermodynamics), and then, in the absence of work, only in the direction of the colder body (as per the second law of thermodynamics). The zeroth law of thermodynamics is a generalized statement about thermal Equilibrium between bodies in contact The second law of Thermodynamics is an expression of the universal law of increasing Entropy, stating that the entropy of an Isolated system which The temperature and phase of a substance subject to heat transfer are determined by latent heat and heat capacity. In Thermochemistry, latent heat is the amount of Energy in the form of Heat released or absorbed by a substance during a change of phase Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the Temperature of a unit quantity A related term is thermal energy, loosely defined as the energy of a body that increases with its temperature. Thermal energy is the sum of the sensible energy and latent energy. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature

Heat from the sun is the driving force of life. The Sun (Sol is the Star at the center of the Solar System. In Physics, a force is whatever can cause an object with Mass to Accelerate. Life is a state that distinguishes Organisms from non-living objects such as non-life and dead organisms being manifested by growth through Metabolism The science of heat and its relation to work is thermodynamics. Science (from the Latin scientia, meaning " Knowledge " or "knowing" is the effort to discover, and increase human understanding In Thermodynamics, work is the quantity of Energy transferred from one system to another without an accompanying transfer of Entropy. In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " Heat flow can be created many ways. In thermal physics, heat transfer is the passage of Thermal energy from a hot to a colder body

## Overview

The first law of thermodynamics states that the energy of a closed system is conserved. In Thermodynamics, the first law of thermodynamics is an expression of the more universal physical law of the Conservation of energy. A Closed system is a System in the state of being isolated from the environment Therefore, to change the energy of a system, energy must be transferred to or from the system. Heat and work are the only two mechanisms by which energy can be transferred to or from a control mass. Heat is the transfer of energy caused by the temperature difference. The unit for the amount of energy transferred by heat in the International System of Units SI is the joule (J), though the British Thermal Unit and the calorie are still occasionally used in the United States. SI derived units are part of the SI system of measurement units and are derived from the seven SI base units They are derived from SI basic units/defined The joule (written in lower case ˈdʒuːl or /ˈdʒaʊl/ (symbol J) is the SI unit of Energy measuring heat, Electricity This article is about the unit of energy For its use in Nutrition and Food labelling regulations, see the article on Food energy. The unit for the rate of heat transfer is the watt (W = J/s). The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second.

Heat Q can flow across the boundary of the system and thus change its internal energy U. In Thermodynamics, a thermodynamic system, originally called a working substance, is defined as that part of the universe that is under consideration In Thermodynamics, the internal energy of a Thermodynamic system, or a body with well-defined boundaries, denoted by  U, or sometimes

Heat transfer is a path function (process quantity), as opposed to a point function (state quantity). A process function (or a process quantity) is a Physical quantity that describes the Transition of a System from an Equilibrium state In Thermodynamics, a state function, state quantity, or a function of state, is a property of a system that depends only on the current Heat flows between systems that are not in thermal equilibrium with each other; it spontaneously flows from the areas of high temperature to areas of low temperature. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature When two bodies of different temperature come into thermal contact, they will exchange internal energy until their temperatures are equalized; that is, until they reach thermal equilibrium. In Thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium Mechanical equilibrium, and The adjective hot is used as a relative term to compare the object’s temperature to that of the surroundings (or that of the person using the term). The term heat is used to describe the flow of energy. In the absence of work interactions, the heat that is transferred to an object ends up getting stored in the object in the form of internal energy.

A red-hot iron rod from which heat transfer to the surrounding environment will be primarily through radiation. In thermal physics, heat transfer is the passage of Thermal energy from a hot to a colder body Thermal radiation is Electromagnetic radiation emitted from the surface of an object which is due to the object's Temperature.

Specific heat is defined as the amount of energy that has to be transferred to or from one unit of mass or mole of a substance to change its temperature by one degree. Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the Temperature of a unit quantity Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object The mole (symbol mol) is a unit of Amount of substance: it is an SI base unit, and almost the only unit to be used to measure this The term degree is used in several scales of Temperature. The symbol ° is usually used followed by the initial letter(s of the unit for example “°C” Specific heat is a property, which means that it depends on the substance under consideration and its state as specified by its properties. Fuels, when burned, release much of the energy in the chemical bonds of their molecules. Fuel is any material that is burned or altered in order to obtain energy Upon changing from one phase to another, a pure substance releases or absorbs heat without its temperature changing. The amount of heat transfer during a phase change is known as latent heat and depends primarily on the substance and its state. In Thermochemistry, latent heat is the amount of Energy in the form of Heat released or absorbed by a substance during a change of phase

### Thermal energy

See main article: Thermal energy

Thermal energy is a term often confused with that of heat. Thermal energy is the sum of the sensible energy and latent energy. Loosely speaking, when heat is added to a thermodynamic system its thermal energy increases and when heat is withdrawn its thermal energy decreases. In Thermodynamics, a thermodynamic system, originally called a working substance, is defined as that part of the universe that is under consideration In this point of view, objects that are hot are referred to as being in possession of a large amount of thermal energy, whereas cold objects possess little thermal energy. Thermal energy then is often mistakenly defined as being synonym for the word heat. This, however, is not the case: an object cannot possess heat, but only energy. The term "thermal energy" when used in conversation is often not used in a strictly correct sense, but is more likely to be only used as a descriptive word. In physics and thermodynamics, the words “heat”, “internal energy”, “work”, "enthalpy" (heat content), "entropy", "external forces", etc. In Thermodynamics, the internal energy of a Thermodynamic system, or a body with well-defined boundaries, denoted by  U, or sometimes  In Thermodynamics, work is the quantity of Energy transferred from one system to another without an accompanying transfer of Entropy. In Thermodynamics and molecular chemistry, the enthalpy (denoted as H, h, or rarely as χ) is a quotient or description of In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy In Physics, a force is whatever can cause an object with Mass to Accelerate. , which can be defined exactly, i. e. without recourse to internal atomic motions and vibrations, tend to be preferred and used more often than the term "thermal energy", which is difficult to define.

## History

Main article: history of heat. In the History of science, the history of Heat traces its origins to the first Hominids to make Fire and to speculate on its operation and meaning

In the history of science, the history of heat traces its origins from the first hominids to make fire and to speculate on its operation and meaning to modern day particle physicists who study the sub-atomic nature of heat. Science is a body of empirical, theoretical, and practical knowledge about the natural world, produced by a global community of researchers A hominid is any member of the biological family Hominidae (the "great apes" including the extinct and extant Humans Chimpanzees Fire is the heat and light energy released during a Chemical reaction, in particular a combustion reaction. Particle physics is a branch of Physics that studies the elementary constituents of Matter and Radiation, and the interactions between them In short, the phenomenon of heat and its definition evolved from mythological theories of fire, to heat, to terra pinguis, phlogiston, to fire air, to caloric, to the theory of heat, to the mechanical equivalent of heat, to thermo-dynamics (sometimes called energetics) to thermodynamics. Fire is the heat and light energy released during a Chemical reaction, in particular a combustion reaction. The phlogiston theory (from the Ancient Greek φλογιστόν phlŏgistón "burning up" from φλόξ phlóx "fire" first stated In the history of chemistry fire air was postulated to be one of two fluids of common air In the history of Science, the theory of heat or mechanical theory of heat was a theory introduced predominantly in 1824 by the French physicist Sadi Carnot In the History of science, the mechanical equivalent of heat was a Concept that played an important part in the development and acceptance of the Conservation In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " Energetics is the scientific study of energy flows and storages under transformation In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " The history of heat, then, is a precursor for developments and theories in the history of thermodynamics. The history of thermodynamics is a fundamental strand in the History of physics, the History of chemistry, and the History of science in general

## Notation

The total amount of energy transferred through heat transfer is conventionally abbreviated as Q. The conventional sign convention is that when a body releases heat into its surroundings, Q < 0 (-); when a body absorbs heat from its surroundings, Q > 0 (+). Heat transfer rate, or heat flow per unit time, is denoted by:

$\dot{Q} = {dQ\over dt} \,\!$.

It is measured in watts. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. Heat flux is defined as rate of heat transfer per unit cross-sectional area, and is denoted q, resulting in units of watts per square metre, though slightly different notation conventions can be used.

### Entropy

In 1854, German physicist Rudolf Clausius defined the second fundamental theorem (the second law of thermodynamics) in the mechanical theory of heat (thermodynamics): "if two transformations which, without necessitating any other permanent change, can mutually replace one another, be called equivalent, then the generations of the quantity of heat Q from work at the temperature T, has the equivalence-value:"[3][4]

$\frac {Q}{T}$

In 1865, he came to define this ratio as entropy symbolized by S, such that, for a closed, stationary system:

$\Delta S = \frac {Q}{T}$

and thus, by reduction, quantities of heat δQ (an inexact differential) are defined as quantities of TdS (an exact differential):

$\delta Q = T dS \,$

In other words, the entropy function S facilitates the quantification and measurement of heat flow through a thermodynamic boundary. Rudolf Julius Emanuel Clausius (Born Rudolf Gottlieb, January 2, 1822 &ndash August 24, 1888) was a German Physicist The second law of Thermodynamics is an expression of the universal law of increasing Entropy, stating that the entropy of an Isolated system which In the history of Science, the theory of heat or mechanical theory of heat was a theory introduced predominantly in 1824 by the French physicist Sadi Carnot In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " In Thermodynamics, work is the quantity of Energy transferred from one system to another without an accompanying transfer of Entropy. In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy In Thermodynamics, an inexact differential or imperfect differential is any quantity particularly Heat Q and work W that are not State In Mathematics, a differential dQ is said to be exact, as contrasted with an Inexact differential, if the differentiable function In Thermodynamics, a boundary is a real or imaginary volumetric demarcation region drawn around a Thermodynamic system across which quantities such as Heat

## Definitions

In modern terms, heat is concisely defined as energy in transit. Scottish physicist James Clerk Maxwell, in his 1871 classic Theory of Heat, was one of the first to enunciate a modern definition of “heat”. James Clerk Maxwell (13 June 1831 &ndash 5 November 1879 was a Scottish mathematician and theoretical physicist. In short, Maxwell outlined four stipulations on the definition of heat. One, it is “something which may be transferred from one body to another”, as per the second law of thermodynamics. The second law of Thermodynamics is an expression of the universal law of increasing Entropy, stating that the entropy of an Isolated system which Two, it can be spoken of as a “measurable quantity”, and thus treated mathematically like other measurable quantities. Three, it “can not be treated as a substance”; for it may be transformed into something which is not a substance, e. g. mechanical work. In Physics, mechanical work is the amount of Energy transferred by a Force. Lastly, it is “one of the forms of energy”. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Similar such modern, succinct definitions of heat are as follows:

• In a thermodynamic sense, heat is never regarded as being stored within a body. Like work, it exists only as energy in transit from one body to another; in thermodynamic terminology, between a system and its surroundings. When energy in the form of heat is added to a system, it is stored not as heat, but as kinetic and potential energy of the atoms and molecules making up the system. [2]
• The noun heat is defined only during the process of energy transfer by conduction or radiation. [5]
• Heat is defined as any spontaneous flow of energy from one object to another, caused by a difference in temperature between two objects. [6]
• Heat may be defined as energy in transit from a high-temperature object to a lower-temperature object. [7]
• Heat as an interaction between two closed systems without exchange of work is a pure heat interaction when the two systems, initially isolated and in a stable equilibrium, are placed in contact. The energy exchanged between the two systems is then called heat. [8]
• Heat is a form of energy possessed by a substance by virtue of the vibrational movement, i. e. kinetic energy, of its molecules or atoms. [9]
• Heat is the transfer of energy between substances of different temperatures.

## Thermodynamics

### Internal energy

Heat is related to the internal energy U of the system and work W done by the system by the first law of thermodynamics:

$\Delta U = Q - W \$

which means that the energy of the system can change either via work or via heat flows across the boundary of the thermodynamic system. In Thermodynamics, the internal energy of a Thermodynamic system, or a body with well-defined boundaries, denoted by  U, or sometimes  In Thermodynamics, work is the quantity of Energy transferred from one system to another without an accompanying transfer of Entropy. In Thermodynamics, the first law of thermodynamics is an expression of the more universal physical law of the Conservation of energy. In Thermodynamics, a thermodynamic system, originally called a working substance, is defined as that part of the universe that is under consideration In more detail, Internal energy is the sum of all microscopic forms of energy of a system. In Thermodynamics, the internal energy of a Thermodynamic system, or a body with well-defined boundaries, denoted by  U, or sometimes  It is related to the molecular structure and the degree of molecular activity and may be viewed as the sum of kinetic and potential energies of the molecules; it comprises the following types of energies:[10]

TypeComposition of Internal Energy (U)
Sensible energythe portion of the internal energy of a system associated with kinetic energies (molecular translation, rotation, and vibration; electron translation and spin; and nuclear spin) of the molecules. In Thermodynamics, the internal energy of a Thermodynamic system, or a body with well-defined boundaries, denoted by  U, or sometimes  Sensible heat is Potential energy in the form of thermal energy or Heat. In Thermodynamics, the internal energy of a Thermodynamic system, or a body with well-defined boundaries, denoted by  U, or sometimes
Latent energythe internal energy associated with the phase of a system. In Thermochemistry, latent heat is the amount of Energy in the form of Heat released or absorbed by a substance during a change of phase In the Physical sciences a phase is a Set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties
Chemical energythe internal energy associated with the atomic bonds in a molecule. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic
Nuclear energythe tremendous amount of energy associated with the strong bonds within the nucleus of the atom itself. Nuclear Energy is released by the splitting (fission or merging together (fusion of the nuclei of Atom (s Nuclear Energy is released by the splitting (fission or merging together (fusion of the nuclei of Atom (s
Energy interactionsthose types of energies not stored in the system (e. In Physics, a fundamental interaction or fundamental force is a mechanism by which particles interact with each other and which cannot be explained in terms g. heat transfer, mass transfer, and work), but which are recognized at the system boundary as they cross it, which represent gains or losses by a system during a process. In thermal physics, heat transfer is the passage of Thermal energy from a hot to a colder body Mass transfer is the phrase commonly used in engineering for physical processes that involve molecular and convective transport of Atoms and Molecules In Thermodynamics, a thermodynamic system, originally called a working substance, is defined as that part of the universe that is under consideration
Thermal energythe sum of sensible and latent forms of internal energy. Thermal energy is the sum of the sensible energy and latent energy.

The transfer of heat to an ideal gas at constant pressure increases the internal energy and performs boundary work (i. e. allows a control volume of gas to become larger or smaller), provided the volume is not constrained. Returning to the first law equation and separating the work term into two types, "boundary work" and "other" (e. In Thermodynamics, the first law of thermodynamics is an expression of the more universal physical law of the Conservation of energy. g. shaft work performed by a compressor fan), yields the following:

$\Delta U + W_{boundary} = Q - W_{other}\$

This combined quantity ΔU + Wboundary is enthalpy, H, one of the thermodynamic potentials. In Thermodynamics and molecular chemistry, the enthalpy (denoted as H, h, or rarely as χ) is a quotient or description of A thermodynamic potential is a Scalar potential function used to represent the Thermodynamic state of a system. Both enthalpy, H, and internal energy, U are state functions. In Thermodynamics, a state function, state quantity, or a function of state, is a property of a system that depends only on the current State functions return to their initial values upon completion of each cycle in cyclic processes such as that of a heat engine. A heat engine is a physical or theoretical device that converts Thermal energy to mechanical output In contrast, neither Q nor W are properties of a system and need not sum to zero over the steps of a cycle. The infinitesimal expression for heat, δQ, forms an inexact differential for processes involving work. In Thermodynamics, an inexact differential or imperfect differential is any quantity particularly Heat Q and work W that are not State However, for processes involving no change in volume, applied magnetic field, or other external parameters, δQ, forms an exact differential. In Mathematics, a differential dQ is said to be exact, as contrasted with an Inexact differential, if the differentiable function Likewise, for adiabatic processes (no heat transfer), the expression for work forms an exact differential, but for processes involving transfer of heat it forms an inexact differential. In Mathematics, a differential dQ is said to be exact, as contrasted with an Inexact differential, if the differentiable function In Thermodynamics, an inexact differential or imperfect differential is any quantity particularly Heat Q and work W that are not State

### Heat capacity

For a simple compressible system such as an ideal gas inside a piston, the changes in enthalpy and internal energy can be related to the heat capacity at constant pressure and volume, respectively. Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the Temperature of a unit quantity Constrained to have constant volume, the heat, Q, required to change its temperature from an initial temperature, T0, to a final temperature, Tf is given by:

$Q = \int_{T_0}^{T_f}C_v\,dT = \Delta U\,\!$

Removing the volume constraint and allowing the system to expand or contract at constant pressure:

$Q = \ \Delta U + \int_{V_0}^{V_f}P\,dV = \ \Delta H = \int_{T_0}^{T_f}C_p\,dT \,\!$

For incompressible substances, such as solids and liquids, the distinction between the two types of heat capacity disappears, as no work is performed. A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of Heat capacity is an extensive quantity and as such is dependent on the number of molecules in the system. In the Physical sciences an intensive property (also called a bulk property) is a Physical property of a system that does not depend on the It can be represented as the product of mass, m , and specific heat capacity, $c_s \,\!$ according to:

$C_p = mc_s \,\!$

or is dependent on the number of moles and the molar heat capacity, $c_n \,\!$ according to:

$C_p = nc_n \,\!$

The molar and specific heat capacities are dependent upon the internal degrees of freedom of the system and not on any external properties such as volume and number of molecules. Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the Temperature of a unit quantity The mole (symbol mol) is a unit of Amount of substance: it is an SI base unit, and almost the only unit to be used to measure this

The specific heats of monatomic gases (e. g. , helium) are nearly constant with temperature. Diatomic gases such as hydrogen display some temperature dependence, and triatomic gases (e. g. , carbon dioxide) still more.

In liquids at sufficiently low temperatures, quantum effects become significant. An example is the behavior of bosons such as helium-4. In Particle physics, bosons are particles which obey Bose-Einstein statistics; they are named after Satyendra Nath Bose and Albert Einstein For such substances, the behavior of heat capacity with temperature is discontinuous at the Bose-Einstein condensation point. A Bose–Einstein condensate (BEC is a State of matter of Bosons confined in an external Potential and cooled to Temperatures very near to

The quantum behavior of solids is adequately characterized by the Debye model. The debye (symbol D) is a non- SI, CGS unit of electrical dipole moment. At temperatures well below the characteristic Debye temperature of a solid lattice, its specific heat will be proportional to the cube of absolute temperature. For low-temperature metals, a second term is needed to account for the behavior of the conduction electrons, an example of Fermi-Dirac statistics. In Statistical mechanics, Fermi-Dirac statistics is a particular case of Particle statistics developed by Enrico Fermi and Paul Dirac that

### Changes of phase

The boiling point of water, at sea level and normal atmospheric pressure and temperature, will always be at nearly 100 °C, no matter how much heat is added. Water is a common Chemical substance that is essential for the survival of all known forms of Life. Mean sea level (MSL is the average (mean height of the Sea, with reference to a suitable reference surface The extra heat changes the phase of the water from liquid into water vapor. General properties of water vapor Evaporation/sublimation Whenever a water molecule leaves a surface it is said to have evaporated The heat added to change the phase of a substance in this way is said to be "hidden" and thus it is called latent heat (from the Latin latere meaning "to lie hidden"). In Thermochemistry, latent heat is the amount of Energy in the form of Heat released or absorbed by a substance during a change of phase Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. Latent heat is the heat per unit mass necessary to change the state of a given substance, or:

$L = \frac{Q}{\Delta m} \,\!$

and

$Q = \int_{M_0}^{M} L\,dm.$

Note that, as pressure increases, the L rises slightly. Here, Mo is the amount of mass initially in the new phase, and M is the amount of mass that ends up in the new phase. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object Also,L generally does not depend on the amount of mass that changes phase, so the equation can normally be written:

Q = LΔm.

Sometimes L can be time-dependent if pressure and volume are changing with time, so that the integral can be written as:

$Q = \int L\frac{dm}{dt}dt.$

## Heat transfer mechanisms

Main article: Heat transfer

Heat tends to move from a high-temperature region to a low-temperature region. In thermal physics, heat transfer is the passage of Thermal energy from a hot to a colder body This heat transfer may occur by the mechanisms of conduction and radiation. Heat conduction or thermal conduction is the spontaneous transfer of thermal energy through matter from a region of higher Temperature to a region of lower Thermal radiation is Electromagnetic radiation emitted from the surface of an object which is due to the object's Temperature. In engineering, the term convective heat transfer is used to describe the combined effects of conduction and fluid flow and is regarded as a third mechanism of heat transfer. Engineering is the Discipline and Profession of applying technical and scientific Knowledge and Convection in the most general terms refers to the movement of molecules within Fluids (i

### Conduction

Conduction is the most significant means of heat transfer in a solid. Heat conduction or thermal conduction is the spontaneous transfer of thermal energy through matter from a region of higher Temperature to a region of lower On a microscopic scale, conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their energy (heat) to these neighboring atoms. In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by In insulators the heat flux is carried almost entirely by phonon vibrations. The term thermal insulation can refer to materials used to reduce the rate of Heat transfer, or the methods and processes used to reduce heat transfer In Physics, a phonon is a quantized mode of vibration occurring in a rigid crystal lattice, such as the Atomic lattice of a Solid

Fire test used to test the heat transfer through firestops and penetrants used in construction listing and approval use and compliance. A fire test is a means of determining whether or not Fire protection products meet minimum performance criteria as set out in a Building code or other applicable legislation A firestop is a Passive fire protection System of various components used to seal openings and joints in fire-resistance rated wall In the fields of Architecture and Civil engineering, construction is a process that consists of the Building or assembling of Infrastructure Listing and approval use and compliance is the activity of adhering to all the requirements of installing and/or using safety-related products and items in conformance with an active

The "electron fluid" of a conductive metallic solid conducts nearly all of the heat flux through the solid. In Science and engineering, a conductor is a material which contains movable Electric charges. Phonon flux is still present, but carries less than 1% of the energy. Electrons also conduct electric current through conductive solids, and the thermal and electrical conductivities of most metals have about the same ratio. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. In Physics, thermal conductivity, k is the property of a material that indicates its ability to conduct Heat. Electrical conductivity or specific conductivity is a measure of a material's ability to conduct an Electric current. The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across A good electrical conductor, such as copper, usually also conducts heat well. Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 The Peltier-Seebeck effect exhibits the propensity of electrons to conduct heat through an electrically conductive solid. The thermoelectric effect is the direct conversion of temperature differences to electric Voltage and vice versa Thermoelectricity is caused by the relationship between electrons, heat fluxes and electrical currents. Thermoelectricity ( Thermo - Electricity) refers to a class of phenomena in which a Temperature difference creates an Electric potential or an electric

### Convection

Convection is usually the dominant form of heat transfer in liquids and gases. Convection in the most general terms refers to the movement of molecules within Fluids (i This is a term used to characterize the combined effects of conduction and fluid flow. In convection, enthalpy transfer occurs by the movement of hot or cold portions of the fluid together with heat transfer by conduction. In Thermodynamics and molecular chemistry, the enthalpy (denoted as H, h, or rarely as χ) is a quotient or description of Commonly an increase in temperature produces a reduction in density. Hence, when water is heated on a stove, hot water from the bottom of the pan rises, displacing the colder more dense liquid which falls. Mixing and conduction result eventually in a nearly homogenous density and even temperature. Two types of convection are commonly distinguished, free convection, in which gravity and buoyancy forces drive the fluid movement, and forced convection, where a fan, stirrer, or other means is used to move the fluid. Buoyant convection is due to the effects of gravity, and hence does not occur in microgravity environments. In Physics, buoyancy ( BrE IPA: /ˈbɔɪənsi/ is the upward Force on an object produced by the surrounding liquid or gas in which it is

Radiation is the only form of heat transfer that can occur in the absence of any form of medium; thus it is the only means of heat transfer through a vacuum. Thermal radiation is Electromagnetic radiation emitted from the surface of an object which is due to the object's Temperature. This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. Thermal radiation is a direct result of the movements of atoms and molecules in a material. Since these atoms and molecules are composed of charged particles (protons and electrons), their movements result in the emission of electromagnetic radiation, which carries energy away from the surface. The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. At the same time, the surface is constantly bombarded by radiation from the surroundings, resulting in the transfer of energy to the surface. Since the amount of emitted radiation increases with increasing temperature, a net transfer of energy from higher temperatures to lower temperatures results.

The power that a black body emits at various frequencies is described by Planck's law. In Physics, a black body is an object that absorbs all light that falls on it For a general introduction see Black body. In Physics, Planck's law describes the spectral radiance of Electromagnetic radiation For any given temperature, there is a frequency fmax at which the power emitted is a maximum. Wien's displacement law, and the fact that the frequency of light is inversely proportional to its wavelength in vacuum, mean that the peak frequency fmax is proportional to the absolute temperature T of the black body. The photosphere of the Sun, at a temperature of approximately 6000 K, emits radiation principally in the visible portion of the spectrum. The earth's atmosphere is partly transparent to visible light, and the light reaching the earth's surface is absorbed or reflected. The earth's surface emits the absorbed radiation, approximating the behavior of a black body at 300 K with spectral peak at fmax. At these lower frequencies, the atmosphere is largely opaque and radiation from the earth's surface is absorbed or scattered by the atmosphere. Though some radiation escapes into space, it is absorbed and subsequently re-emitted by atmospheric gases. It is this spectral selectivity of the atmosphere that is responsible for the planetary greenhouse effect. The Greenhouse effect refers to the change in the Thermal equilibrium temperature of a planet or moon by the presence of an Atmosphere containing gas that absorbs

The common household lightbulb has a spectrum overlapping the blackbody spectra of the sun and the earth. The incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric Light that works by Incandescence, (a general A portion of the photons emitted by a tungsten light bulb filament at 3000K are in the visible spectrum. Color temperature is a characteristic of Visible light that has important applications in lighting photography videography publishing and other fields However, most of the energy is associated with photons of longer wavelengths; these will not help a person see, but will still transfer heat to the environment, as can be deduced empirically by observing a household incandescent lightbulb. Whenever EM radiation is emitted and then absorbed, heat is transferred. This principle is used in microwave ovens, laser cutting, and RF hair removal. A microwave oven, or a microwave, is a Kitchen appliance that cooks or heats Food by Dielectric heating. Laser cutting is a technology that uses a Laser to cut materials and is typically used for industrial manufacturing applications Electrology is the practice of electrical depilation to permanently remove human Hair.

Heat exposure as part of a fire test for firestop products. A fire test is a means of determining whether or not Fire protection products meet minimum performance criteria as set out in a Building code or other applicable legislation A firestop is a Passive fire protection System of various components used to seal openings and joints in fire-resistance rated wall

### Other heat transfer mechanisms

• Latent heat: Transfer of heat through a physical change in the medium such as water-to-ice or water-to-steam involves significant energy and is exploited in many ways: steam engine, refrigerator etc. In Thermochemistry, latent heat is the amount of Energy in the form of Heat released or absorbed by a substance during a change of phase A steam engine is a Heat engine that performs Mechanical work using Steam as its Working fluid. A refrigerator (often called a " fridge " for short is a cooling appliance comprising a thermally insulated compartment and a Heat pump - (see latent heat of fusion)
• Heat pipes: Using latent heat and capillary action to move heat, heat pipes can carry many times as much heat as a similar-sized copper rod. The standard Enthalpy of fusion (symbol \Delta{}H_{fus} also known as the heat of fusion or specific melting heat, is the amount of A heat pipe is a heat transfer mechanism that can transport large quantities of heat with a very small difference in Temperature between the hotter and colder interfaces Originally invented for use in satellites, they are starting to have applications in personal computers. This article is about artificial satellites For natural satellites also known as moons see Natural satellite. A personal computer ( PC) is any Computer whose original sales price size and capabilities make it useful for individuals and which is intended to be operated

## Heat dissipation

In cold climates, houses with their heating systems form dissipative systems. In spite of efforts to insulate such houses to reduce heat losses to their exteriors, considerable heat is lost, or dissipated, from them, which can make their interiors uncomfortably cool or cold. For the comfort of its inhabitants, the interior of a house must be maintained out of thermal equilibrium with its external surroundings. In effect, domestic residences are oases of warmth in a sea of cold and the thermal gradient between the inside and outside is often quite steep. This can lead to problems such as condensation and uncomfortable draughts (drafts) which, if left unaddressed, can cause structural damage to the property. Condensation is the change of the physical state of aggregation (or simply state of matter from gaseous phase into liquid phase This is why modern insulation techniques are required to reduce heat loss.

In such a house, a thermostat is a device capable of starting the heating system when the house's interior falls below a set temperature, and of stopping that same system when another (higher) set temperature has been achieved. A thermostat is a device for regulating the Temperature of a System so that the system's temperature is maintained near a desired setpoint Thus the thermostat controls the flow of energy into the house, that energy eventually being dissipated to the exterior.

## References

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