Evaporation is the process of the phase transition of a substance from a liquid state to a vaporous or gaseous one , occurring on the surface of a substance. The evaporation process is the reverse of the condensation process (transition from vapor to liquid state). Upon evaporation from the surface of a liquid or solid, particles (molecules, atoms) fly out (come off), and their kinetic energy must be sufficient to complete the work necessary to overcome the attractive forces of other liquid molecules.
Content
- 1 General characteristics
- 2 molecular level
- 3 See also
- 4 Literature
- 5 Links
General characteristics
The evaporation of a solid is called sublimation (sublimation), and the vaporization in a liquid volume is called boiling. Evaporation is an endothermic process in which the heat of phase transition is absorbed - the heat of evaporation spent on overcoming the molecular cohesion forces in the liquid phase and on the work of expansion when the liquid is converted into steam.
The evaporation process depends on the intensity of the thermal motion of the molecules : the faster the molecules move, the faster the evaporation. In addition, the rate of external (relative to the substance) diffusion , as well as the properties of the substance itself, affect evaporation: for example, alcohols evaporate faster than water. An important factor is also the surface area of the liquid with which evaporation occurs: from a narrow glass it will occur more slowly than from a wide plate.
Molecular Level
Consider this process at the molecular level: molecules that have sufficient energy (speed) to overcome the attraction of neighboring molecules (that is, the fastest) break out beyond the boundaries of a substance (liquid). In this case, the average energy of the remaining molecules becomes smaller (the liquid cools down). For example, a very hot liquid: we blow to its surface to cool, while we accelerate the evaporation process.
See also
- Sublimation
- Vaporization
- Boiling
Literature
- Evaporation // Brockhaus and Efron Encyclopedic Dictionary : in 86 volumes (82 volumes and 4 additional). - SPb. , 1890-1907.
- Berman L.D. Evaporative cooling of circulating water, 2nd ed., M.-L., 1957.
- Fuchs N.A. Evaporation and growth of droplets in a gaseous medium, M., 1958.
- Bird R., Stuart W., Lightfoot E. Transport Phenomena, trans. from English., M., 1974.
- Berman L. D. Theoretical Foundations of Chem. Technology, 1974, v. 8, No. 6, p. 811-22.
- Sherwood T., Pigford R., Wilkie C. Mass transfer, trans. from English., M., 1982. L.D. Berman.