Vaporization

Vaporization is the process by which a substance transitions from a liquid to a gaseous phase. It includes evaporation, where molecules escape from a liquid’s surface at temperatures below its boiling point, and boiling, where vapor forms within the liquid as its vapor pressure equals the surrounding pressure. Some definitions also include sublimation as a form of vaporization of a solid to gas, though sublimation is typically treated as a separate phase transition.

Energy input is required; the amount per mole is the latent heat of vaporization. Evaporation is driven by molecular escape at the surface and can occur at any temperature; boiling occurs when the liquid reaches its boiling point and the vapor pressure matches the ambient pressure, permitting bubble formation. External pressure lowers or raises the boiling point. The rate of vaporization depends on temperature, surface area, agitation, airflow, and the presence of impurities or dissolved substances.

Applications of vaporization include distillation, which separates components by differing boiling points; drying and desalination; and evaporative cooling, as seen in sweating or industrial cooling towers. In chemical processing and food production, evaporators remove solvent or concentrate solutions.

Vapors may be hazardous: some are flammable, toxic, or corrosive. Vapor pressure is a key property that influences evaporation rate and exposure risk; safe handling requires adequate ventilation and avoidance of ignition sources where appropriate.

Measurement and theory: the latent heat of vaporization varies with temperature; the Clausius–Clapeyron relation describes how vapor pressure changes with temperature, and the Antoine equation provides practical estimates of vapor pressure for many liquids.