# Heat of Vaporization

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## 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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

## 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
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 heat of vaporization is defined as the minimum amount of energy required to evaporate a unit of mass of water bound to the biological structure of agricultural products (Correa et al., 1998; Sousa et al., 2016).
The third method started with determining a new function for the latent heat of vaporization, by comparing the saturation vapor pressures derived from the Clausius-Clapeyron equation (which assumes temperature-dependent variable values of [l.sub.[upsilon]]) to the saturation vapor pressures derived for the same temperature using an advanced form of the equation (which assumes a fixed value of [l.sub.[upsilon]], called [l.sub.[upsilon]0]):
The calculated heat of vaporization for naphthalene was lower than the literature value.
The total energy requirement (Q) consists of the sensible heat required to heat the substrate from room temperature to its boiling point and the latent heat of vaporization.
For large-scale power generation, relatively small discrepancies in the calculation of key properties, such as the heat of vaporization, can translate into a difference of hundreds of thousands of dollars in the values calculated for the performance of boilers and turbines.
By typing 'F1', you can call up a menu that provides information on melting point, boiling point, density, heat of fusion, heat of vaporization, heat capacity, first through fourth ionization energies, electrical resistivity, atomic radius, ionic radii, covalent radius, van der Waal's radius, oxidation states, natural isotopes, or discovery for the current element.
Latent heat of vaporization of water is 974 Btu/lb = 540 kcal/kg
P* is a measure of the volatility per monomer unit, since it is equal to the heat of vaporization per unit volume.
Because water absorbs a considerable amount of energy as it is converted from a liquid to a vapor, this energy, the latent heat of vaporization, is lost.
For liquids, Hildebrand parameter can be calculated through their heat of vaporization, however, polymers usually degrade before it is possible to measure heat of vaporization.

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