Editing Enthalpy (section)

===Enthalpy changes===
An enthalpy change describes the change in enthalpy observed in the constituents of a thermodynamic system when undergoing a transformation or chemical reaction. It is the difference between the enthalpy after the process has completed, i.e. the enthalpy of the [[Product (chemistry)|products]] assuming that the reaction goes to completion, and the initial enthalpy of the system, namely the reactants. These processes are specified solely by their initial and final states, so that the enthalpy change for the reverse is the negative of that for the forward process.

A common standard enthalpy change is the [[enthalpy of formation]], which has been determined for a large number of substances. Enthalpy changes are routinely measured and compiled in chemical and physical reference works, such as the [[CRC Handbook of Chemistry and Physics]]. The following is a selection of enthalpy changes commonly recognized in thermodynamics.

When used in these recognized terms the qualifier ''change'' is usually dropped and the property is simply termed ''enthalpy of "process"''. Since these properties are often used as reference values, it is very common to quote them for a standardized set of environmental parameters, or [[standard conditions]], including:
* A [[pressure]] of one atmosphere (1&nbsp;atm = 1013.25&nbsp;hPa) or 1&nbsp;bar
* A [[temperature]] of 25&nbsp;°C = 298.15&nbsp;K
* A [[concentration]] of 1.0&nbsp;[[Molar concentration|M]] when the element or compound is present in solution
* Elements or compounds in their normal physical states, i.e. [[standard state]]
For such standardized values the name of the enthalpy is commonly prefixed with the term ''standard'', e.g. ''standard enthalpy of formation''.

====Chemical properties====
[[Enthalpy of reaction]] is defined as the enthalpy change observed in a constituent of a thermodynamic system when one mole of substance reacts completely.

[[Enthalpy of formation]] is defined as the enthalpy change observed in a constituent of a thermodynamic system when one mole of a compound is formed from its elementary antecedents.

[[Enthalpy of combustion]] is defined as the enthalpy change observed in a constituent of a thermodynamic system when one mole of a substance burns completely with oxygen.

[[Enthalpy of hydrogenation]] is defined as the enthalpy change observed in a constituent of a thermodynamic system when one mole of an unsaturated compound reacts completely with an excess of hydrogen to form a [[Saturated and unsaturated compounds|saturated compound]].

[[Enthalpy of atomization]] is defined as the enthalpy change required to separate one mole of a substance into its constituent [[atom]]s completely.

[[Enthalpy of neutralization]] is defined as the enthalpy change observed in a constituent of a thermodynamic system when one mole of water is formed when an acid and a base react.

Standard [[enthalpy of solution]] is defined as the enthalpy change observed in a constituent of a thermodynamic system when one mole of a solute is dissolved completely in an excess of solvent, so that the solution is at infinite dilution.

Standard enthalpy of [[Denaturation (biochemistry)|denaturation]] is defined as the enthalpy change required to denature one mole of compound.

[[Hydration energy|Enthalpy of hydration]] is defined as the enthalpy change observed when one mole of gaseous ions is completely dissolved in water forming one mole of aqueous ions.

====Physical properties====
[[Enthalpy of fusion]] is defined as the enthalpy change required to completely change the state of one mole of substance from solid to liquid.

[[Enthalpy of vaporization]] is defined as the enthalpy change required to completely change the state of one mole of substance from liquid to gas.

[[Enthalpy of sublimation]] is defined as the enthalpy change required to completely change the state of one mole of substance from solid to gas.

[[Lattice enthalpy]] is defined as the energy required to separate one mole of an ionic compound into separated gaseous ions to an infinite distance apart (meaning no force of attraction).

[[Enthalpy of mixing]] is defined as the enthalpy change upon mixing of two (non-reacting) chemical substances.