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The '''heat of vaporization''', (<math>H_v</math>) is the amount of thermal [[energy] required to convert a  quantity of [[liquid]] into a [[vapor]]. It can be thought of as the energy required to break the
intermolecular bonds within the liquid.
It is also often referred to as the '''latent heat of vaporization''' (s<math>LH_v</math> or <math>L_v</math>) and the '''enthalpy of vaporization''' (symbol <math>H_v</math> or <math>\Delta H_v</math>) and is usually measured and reported at the [[temperature]] corresponding to the [[normal boiling point]] of the liquid. 
== Units ==
Values are usually quoted in [[Joule|J]]/[[Mole (unit)|mol]] or kJ/mol (molar heat of vaporization), although kJ/[[Kilogram|kg]] or J/g (specific heat of vaporization), and older units like [[Calorie|kcal]]/mol, cal/g and [[British thermal unit|Btu]]/[[Pound (mass)|lb]] are sometimes still used, among others.
{{Image|Heat of Vaporization.png|right|325px|Heats of vaporization versus temperature.<ref>[http://www.ddbst.com/new/Default.htm Dortmund Data Bank Online Search]</ref>}}
{{Image|Heat of Vaporization.png|right|325px|Heats of vaporization versus temperature.<ref>[http://www.ddbst.com/new/Default.htm Dortmund Data Bank Online Search]</ref>}}


Revision as of 16:45, 8 September 2009

The heat of vaporization, () is the amount of thermal [[energy] required to convert a quantity of liquid into a vapor. It can be thought of as the energy required to break the intermolecular bonds within the liquid.

It is also often referred to as the latent heat of vaporization (s or ) and the enthalpy of vaporization (symbol or ) and is usually measured and reported at the temperature corresponding to the normal boiling point of the liquid.


Units

Values are usually quoted in J/mol or kJ/mol (molar heat of vaporization), although kJ/kg or J/g (specific heat of vaporization), and older units like kcal/mol, cal/g and Btu/lb are sometimes still used, among others.

(GNU) Diagram: Wilfried Cordes
Heats of vaporization versus temperature.[1]




















Heat of vaporization, normal boiling point and critical
temperature and pressure of various liquids [2][3]
Name Formula Hv Tn Tc Pc
( J/mol ) ( °C ) ( K ) ( K ) ( atm )
Acetic acid C2H4O2 23,700 117.9 391.1 594.8 57.1
Acetone C3H6O 29,100 56.2 329.4 508.7 47.0
Benzene C6H6 30,720 80.0 353.2 562.1 48.6
Butane C4H10 22,440 – 0.5 272.7 425.2 37.5
Carbon tetrachloride CCl4 29,820 76.6 349.8 556.3 45.0
Chloroform CHCl3 29,240 61.1 334.3 536.2 54.0
Cyclohexane C6H12 29,970 80.7 353.9 553.6 40.0
Cyclopentane C5H10 27,300 49.2 322.4 511.8 44.6
Decane C10H22 38,750 174.1 447.3 617.6 20.8
Ethanol C2H6O 38,560 78.2 351.4 516.2 63.0
Hexane C6H14 28.850 68.7 341.9 507.4 29.9
Isobutane C4H10 21,300 – 11.9 261.3 408.2 36.0
Methanol CH4O 35,210 64.7 337.9 513.2 78.5
Octane C8H18 34,410 125.6 398.8 569.2 24.8
Water H20 40,660 100 373.2 647.3 218.3
Notes:
(1) Hv = heat of vaporization at the normal boiling point
(2) Tn = normal boiling point
(3) Tc = critical temperature
(4) Pc = absolute critical pressure









































References

  1. ↑ Dortmund Data Bank Online Search
  2. ↑ J.M. Smith, H.C. Van Ness and N.M. Abbot (2004). Introduction to Chemical Engineering Thermodynamics, 7th Edition. McGraw-Hill. ISBN 0-07-310445-0. 
  3. ↑ Robert C. Weast (Editor) (1976). Perry's Chemical Engineers' Handbook, 56th Edition. CRC Press. ISBN 0-87819-455-X. 
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