Editing Enthalpy of vaporization (section)

{{Short description|Energy to convert a liquid substance to a gas at a given pressure}}
{{Use American English|date = March 2019}}
{{Use dmy dates|date=October 2014}}
{{more footnotes needed|date=March 2016}}
[[Image:Heat of Vaporization (Benzene+Acetone+Methanol+Water).png|thumb|280px|Temperature-dependency of the heats of vaporization for [[water]], [[methanol]], [[benzene]], and [[acetone]]]]

In [[thermodynamics]], the '''enthalpy of vaporization''' (symbol {{math|∆''H''<sub>vap</sub>}}), also known as the ('''latent''') '''heat of vaporization''' or '''heat of evaporation''', is the amount of energy ([[enthalpy]]) that must be added to a [[liquid]] substance to [[Phase transition|transform]] a quantity of that substance into a [[gas]]. The enthalpy of vaporization is a function of the [[pressure]] and temperature at which the transformation ([[vaporization]] or [[evaporation]]) takes place.

The enthalpy of vaporization is often quoted for the [[normal boiling point|normal boiling temperature]] of the substance. Although tabulated values are usually corrected to 298&nbsp;[[Kelvin|K]], that correction is often smaller than the [[Significant figures|uncertainty]] in the measured value.

The heat of vaporization is temperature-dependent, though a constant heat of vaporization can be assumed for small temperature ranges and for [[reduced temperature]] {{math|''T{{sub|r}}'' ≪ 1}}. The heat of vaporization diminishes with increasing temperature and it vanishes completely at a certain point called the [[critical temperature]] ({{math|1=''T{{sub|r}}'' = 1}}). Above the critical temperature, the liquid and [[vapor]] phases are indistinguishable, and the substance is called a [[supercritical fluid]].