Heat of Vaporization


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Related to Heat of Vaporization: heat of sublimation, heat of condensation, Latent heat of vaporization

heat of vaporization

[′hēt əv ‚vā·pə·rə′zā·shən]
(thermodynamics)
The quantity of energy required to evaporate 1 mole, or a unit mass, of a liquid, at constant pressure and temperature. Also known as enthalpy of vaporization; heat of evaporation; latent heat of vaporization.

Heat of Vaporization

 

(or heat of evaporation, latent heat of vaporization), the amount of heat that must be supplied to a substance in an equilibrium constant-pressure and constant-temperature process to convert the substance from the liquid state to the gaseous state. The same amount of heat is liberated when the vapor condenses into a liquid.

Table 1. Heat of vaporization of several substances
Substancetb(°C)Lv(kcal/kg)Lv(j/kg)
Hydrogen ...............–252.61074.48 × 105
Nitrogen ...............–195.847.61.99 × 105
Ethyl alcohol ...............78.42169.05 × 105
Water ...............10053922.6 × 105
Mercury ...............35769.72.82 × 105
Lead ...............17402048.55 × 105
Copper ...............26001,15048.2 × 105
Iron32001,46061.2 × 105

The heat of vaporization is a special case of the heat of a firstorder transition. For a given substance, the heat of vaporization may be determined per unit mass or per mole. In the former case, the heat of vaporization is measured in, for example, joules per kg (J/kg) or kilocalories per kg (kcal/kg). In the latter case, the heat of vaporization may be expressed in joules per mole. The term “molar heat of vaporization” is sometimes applied to the heat of vaporization per mole. Table 1 gives the values of the heat of vaporization per kg Lv for several substances at normal external pressure (760 mm Hg, or 101,325 newtons per m2) and at the boiling point tb.

References in periodicals archive ?
The purpose of this paper is to review previous studies relative to the vaporization of organic wood preservatives from treated wood and to describe how vaporization rates are affected by concentration, heat of vaporization, and surrounding temperature.
Neglecting the enthalpy of the condensed water, the latent heat of vaporization is equal to the specific enthalpy of saturated water vapor.
In this case, the latent heat of vaporization from the primary kiln's water vapor is captured by the heat exchangers and is transferred to the secondary kiln.
P* is a measure of the volatility per monomer unit, since it is equal to the heat of vaporization per unit volume.
25[degrees]C) and the highest latent heat of vaporization among known refrigerants (1370.
In the process, a melt seeded with droplets of a volatile liquid is rapidly decompressed, leading to a dynamic, superheated and supersaturated mixture; then the droplets explosively vaporize, taking their heat of vaporization from the melt and, therefore, homogeneously cooling and expanding it.
That is, its heat capacity and, in the case of water, its heat of vaporization.