Enthalpy of vaporization

The enthalpy change required to convert a liquid into a gas at constant pressure, usually expressed per unit amount of substance. It depends on temperature and the substance.

Vaporization: The phase transition in which a liquid becomes a gas. Enthalpy of vaporization quantifies the enthalpy change for this phase transition.
Enthalpy: A thermodynamic state function equal to internal energy plus pressure multiplied by volume. The vaporization value is the difference in enthalpy between vapor and liquid states.
Evaporative cooling: Cooling caused when high-energy molecules escape from a liquid into a gas. The escaping molecules carry away energy associated with vaporization enthalpy.
Water: The chemical compound H₂O, whose molecules form extensive hydrogen bonds in liquid form. Hydrogen bonding gives water an unusually high vaporization enthalpy among small molecules.
Intermolecular force: An attractive or repulsive interaction between molecules. Separating molecules against their attractions accounts for much of vaporization’s energy demand.
Phase transition: A change between distinct physical states of matter. Vaporization enthalpy describes one specific phase transition.
Boiling point: The temperature at which a liquid’s vapor pressure equals the surrounding pressure. Vaporization enthalpy helps determine how vapor pressure rises toward the boiling condition.
Ethanol: A two-carbon alcohol with the formula C₂H₅OH. Its hydrogen bonding and molecular size produce a vaporization enthalpy distinct from water’s.
Latent heat: Energy transferred during a phase change without changing the substance’s temperature. At constant pressure, vaporization’s latent heat corresponds to its enthalpy change.
Specific latent heat: Energy required per unit mass to change a substance’s phase at specified conditions. It expresses phase-change energy per mass rather than per mole.

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