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In thermodynamics
Thermodynamics

In physics, thermodynamics is the study of the conversion of heat energy into different forms of energy ; different energy conversions into heat energy; and its relation to macroscopic variables such as temperature, pressure, and volume....
, the term exothermic (literally meaning "outside heating") describes a process or reaction that releases energy
Energy

In physics, energy is a scalar physical quantity that describes the amount of Work_ that can be performed by a force. Energy is an attribute of objects and systems that is subject to a conservation law....
 usually in the form of heat
Heat

In physics and thermodynamics, heat is any transfer of energy from one body or thermodynamic system to another due to a difference in temperature....
, but also in form of light
Light

Light, or visible light, is electromagnetic radiation of a wavelength that is Visible spectrum to the human eye , or up to 380?750 nm. In the broader field of physics, light is sometimes used to refer to electromagnetic radiation of all wavelengths, whether visible or not....
 (e.g. a spark, flame, or explosion), electricity
Electricity

Electricity is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena such as lightning and static electricity, but in addition, less familiar concepts such as the electromagnetic field and electromagnetic induction....
 (e.g. a battery), or sound
Sound

Sound is vibration transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a threshold of hearing to be heard, or the sensation stimulated in organs of hearing by such vibrations....
. Its etymology stems from the Greek prefix ex- (meaning "outside") and the Greek word thermein (meaning "to heat"). The term exothermic was first coined by Marcellin Berthelot
Marcellin Berthelot

Marcellin Pierre Eug?ne Berthelot was a French chemist and politician noted in thermochemistry for the Thomsen-Berthelot principle. He synthesized many organic compounds from inorganic substances and so utterly disproved the theory of vitalism....
.






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In thermodynamics
Thermodynamics

In physics, thermodynamics is the study of the conversion of heat energy into different forms of energy ; different energy conversions into heat energy; and its relation to macroscopic variables such as temperature, pressure, and volume....
, the term exothermic (literally meaning "outside heating") describes a process or reaction that releases energy
Energy

In physics, energy is a scalar physical quantity that describes the amount of Work_ that can be performed by a force. Energy is an attribute of objects and systems that is subject to a conservation law....
 usually in the form of heat
Heat

In physics and thermodynamics, heat is any transfer of energy from one body or thermodynamic system to another due to a difference in temperature....
, but also in form of light
Light

Light, or visible light, is electromagnetic radiation of a wavelength that is Visible spectrum to the human eye , or up to 380?750 nm. In the broader field of physics, light is sometimes used to refer to electromagnetic radiation of all wavelengths, whether visible or not....
 (e.g. a spark, flame, or explosion), electricity
Electricity

Electricity is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena such as lightning and static electricity, but in addition, less familiar concepts such as the electromagnetic field and electromagnetic induction....
 (e.g. a battery), or sound
Sound

Sound is vibration transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a threshold of hearing to be heard, or the sensation stimulated in organs of hearing by such vibrations....
. Its etymology stems from the Greek prefix ex- (meaning "outside") and the Greek word thermein (meaning "to heat"). The term exothermic was first coined by Marcellin Berthelot
Marcellin Berthelot

Marcellin Pierre Eug?ne Berthelot was a French chemist and politician noted in thermochemistry for the Thomsen-Berthelot principle. He synthesized many organic compounds from inorganic substances and so utterly disproved the theory of vitalism....
. The opposite of an exothermic process is an endothermic
Endothermic

In thermodynamics, the word endothermic "within-heating" describes a process or reaction that absorbs energy in the form of heat. Its etymology stems from the Greek prefix endo-, meaning ?inside? and the Greek suffix ?thermic, meaning ?to heat?....
 process, one that absorbs energy in the form of heat.

The concept is frequently applied in the physical sciences to chemical reactions, where chemical bond energy
Bond energy

In chemistry, bond energy is a measure of bond strength in a chemical bond. For example the carbon-hydrogen bond energy in methane E is the enthalpy change involved with breaking up one molecule of methane into a carbon atom and 4 hydrogen Radical s divided by 4....
 is converted to thermal energy
Thermal energy

Thermal energy is a form of energy that manifests itself as an increase of temperature. It is also the sum of sensible heat and latent heat....
 (heat).

Overview

Exothermic refers to a transformation in which a system releases energy (heat) to the surroundings:

Q < 0


When the transformation occurs at constant pressure:

?H < 0


and constant volume:

?U < 0


In an adiabatic system (e.g. a system that does not give off heat to the surroundings), an exothermic process results in an increase in temperature.

In chemical reactions, the heat that is released is in the form of electromagnetic energy. The loss of kinetic energy via reacting electrons causes light to be released. This light is equivalent in energy to the stabilization energy of the energy for the chemical reaction, i.e. the bond energy. This light that is released can be absorbed by other molecules in solution to give rise to molecular vibrations or rotations, which gives rise to the classical understanding of heat. In contrast, when endothermic reactions occur, energy is absorbed to place an electron in a higher energy state, such that the electron can associate with another atom to form another chemical complex. The loss of energy within solution is absorbed by the endothermic reaction and therefore is a loss of heat. This is the physical understanding of exothermic and endothermic reactions within solution.

Examples

Some examples of exothermic processes are:
  • Condensation of rain from water vapour
  • Combustion of fuel
    Fuel

    Fuel is any material that is burned or altered in order to obtain energy and to heat or to move an object. Fuel releases its energy either through a chemical reaction means, such as combustion, or nuclear means, such as nuclear fission or nuclear fusion....
    s such as wood
    Wood

    Wood is an organic material; in the strict sense wood is produced as secondary xylem in the stems of woody plants, notably trees but also shrubs, etc....
    , coal
    Coal

    Coal is a readily combustion black or brownish-black sedimentary rock. The harder forms, such as anthracite, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure....
     and oil
    Oil

    An oil is a chemical substance that is in a viscosity liquid state at room temperature or slightly warmer, and is both hydrophobic and lipophilic ....
  • Mixing water and strong acid
    Strong acid

    A strong acid is an acid that ionizes completely in an aqueous solution , or in other terms, with a acid dissociation constant < -1.74. This generally means that in aqueous solution at standard temperature and pressure, the concentration of hydronium ions is equal to the concentration of strong acid introduced to the solution....
    s
  • Mixing alkalis and acids
  • The setting of cement
    Cement

    In the most general sense of the word, a cement is a binder, a substance which sets and hardens independently, and can bind other materials together....
     and concrete
    Concrete

    Concrete is a construction material composed of cement as well as other cementitious materials such as fly ash and slag cement, construction aggregate , water , and Chemistry admixtures....
  • Most polymerisation reactions such as the setting of epoxy resin
  • Thermite
    Thermite

    Thermite is a pyrotechnic composition of a metal powder and a metal oxide, which produces an aluminothermic reaction known as a thermite reaction....
     reaction


Implications for chemical reactions

Chemical exothermic reactions are generally more spontaneous than their counterparts, endothermic reactions. In a thermochemical reaction that is exothermic, the heat may be listed among the products of the reaction.

See also

  • Calorimetry
    Calorimetry

    Calorimetry is the science of measuring the heat of chemical...
  • Chemical thermodynamics
    Chemical thermodynamics

    Chemical thermodynamics is the study of the interrelation of heat and thermodynamic work with chemical reactions or with physical changes of thermodynamic state within the confines of the laws of thermodynamics....
  • Differential scanning calorimetry
    Differential scanning calorimetry

    Differential scanning calorimetry or DSC is a thermal analysis technique in which the difference in the amount of heat required to increase the temperature of a sample and reference are measured as a function of temperature....
  • Endergonic
    Endergonic

    Endergonic means absorbing energy in the form of work. Its etymology stems from the suffix -ergonic, as derived from the Greek root ergon, meaning work , combined with the prefix end-, as derived from the Greek root en, meaning put into....
  • Endergonic reaction
    Endergonic reaction

    In thermochemistry, an endergonic reaction is a chemical reaction in which the standard change in Thermodynamic free energy is positive, and energy is absorbed....
  • Exergonic
    Exergonic

    Exergonic means to release energy in the form of work. Its etymology stems from the suffix -ergonic, as derived from the Greek root ergon, meaning work , combined with the Greek prefix ex-, meaning out of....
  • Exergonic reaction
    Exergonic reaction

    An exergonic reaction is a chemical reaction where the change in the Gibbs free energy is negative, indicating a spontaneous reaction. Symbolically, the release of Gibbs free energy, G, in an exergonic reaction is denoted as...


External links

  • Observe exothermic reactions in a simple experiment