haihtumis

Haihtuminen is the Finnish term for evaporation, the process by which a substance changes from a liquid to a gaseous phase, typically at temperatures below the liquid’s boiling point. It is a surface phenomenon in which molecules at the liquid–air interface acquire enough energy to overcome intermolecular forces and escape as vapor. Evaporation occurs at all temperatures, but its rate increases with higher temperature and slower with factors that reduce the tendency of molecules to leave the surface.

The rate of haihtuminen is influenced by several factors. Temperature and the vapor pressure of the liquid determine how readily molecules escape. A larger surface area provides more molecules at the interface to evaporate. Ambient humidity and air movement affect how quickly vapor is removed from the surface; lower surrounding vapor pressure and better ventilation generally raise the rate. Pressure also plays a role, with lower external pressure enhancing evaporation. The presence of solutes or impurities can lower the liquid’s effective vapor pressure, altering the rate.

Haihtuminen is a key element in natural and technological processes. In the environment it drives the water cycle, drying of soils, and transpiration in plants. In industry it is exploited in drying coatings and foods, solvent reclamation, and distillation. In everyday life, evaporation contributes to cooling effects when liquids absorb latent heat during phase change.

Thermodynamically, evaporation is related to the liquid’s vapor pressure and the latent heat of vaporization. It can be described qualitatively by the difference between the surface vapor pressure and the ambient vapor pressure, and quantitatively through mass-transfer models and, at higher accuracy, equations like Clausius–Clapeyron for vapor pressure versus temperature.