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Temperature-dependency of the heats of vaporization for water, methanol, benzene, and acetone. In thermodynamics, the enthalpy of vaporization (symbol ∆H vap), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy that must be added to a liquid substance to transform a quantity of that substance into a gas.
Latent heat can be understood as hidden energy which is supplied or extracted to change the state of a substance without changing its temperature or pressure. This includes the latent heat of fusion (solid to liquid), the latent heat of vaporization (liquid to gas) and the latent heat of sublimation (solid to gas). [1] [2]
Vaporization (or vapo(u)risation) of an element or compound is a phase transition from the liquid phase to vapor. [1] There are two types of vaporization: evaporation and boiling . Evaporation is a surface phenomenon , whereas boiling is a bulk phenomenon (a phenomenon in which the whole object or substance is involved in the process).
For a liquid–gas transition, is the molar latent heat (or molar enthalpy) of vaporization; for a solid–gas transition, is the molar latent heat of sublimation. If the latent heat is known, then knowledge of one point on the coexistence curve , for instance (1 bar, 373 K) for water, determines the rest of the curve.
L is the latent heat of vaporization at the temperature T, T C is the critical temperature, L 0 is the parameter that is equal to the heat of vaporization at zero temperature (T → 0), tanh is the hyperbolic tangent function. This equation was obtained in 1955 by Yu. I. Shimansky, at first empirically, and later derived theoretically.
For example, latent heat release in atmospheric convection is directly responsible for powering destructive storms such as tropical cyclones and severe thunderstorms. Water vapor is an important greenhouse gas [18] [19] owing to the presence of the hydroxyl bond which strongly absorbs in the infra-red.
J.A. Dean (ed.), Lange's Handbook of Chemistry (15th Edition), McGraw-Hill, 1999; Section 6, Thermodynamic Properties; Table 6.4, Heats of Fusion, Vaporization, and Sublimation and Specific Heat at Various Temperatures of the Elements and Inorganic Compounds
where is the heat or enthalpy of vaporization. Since this is a thermodynamic equation, the symbol refers to the absolute thermodynamic temperature, measured in kelvins (K). The entropy of vaporization is then equal to the heat of vaporization divided by the boiling point: [2] [3]