Condensation: what is it?

Condensation is a fundamental physical phenomenon that occurs when matter passes from one gaseous state in a condensed, solid, or sometimes liquid state. Two essential aspects of this process are liquid condensation, also called liquefaction, and solid condensation, known as crystallization.

Liquid condensation (liquefaction): the gas-liquid transition

Liquid condensation involves the transition from a gas to a liquid. This process typically occurs when the temperature of a gas reaches its saturation point, leading to the formation of liquid droplets. Liquid condensation is the result of the loss of thermal energy of the gas, causing the reduction in molecular velocity and thus promoting liquid molecular aggregation. This phenomenon is ubiquitous in nature, illustrated by the formation of dew, the nucleation of clouds, and the condensation of atmospheric vapors.

Underlying mechanisms: intermolecular forces and temperature

Intermolecular forces play a crucial role in liquid condensation. The molecules of gases, under the influence of intermolecular attractive forces, lose kinetic energy, thus promoting the transition towards a liquid state. Temperature is also a key factor; the more it decreases, the more the molecules slow down, making the transition easier.

Solid condensation (crystallization): gas-solid passage

If in common language the term condensation generally designates the change of gas-liquid state, it remains linked to a shift in gas-solid state for physicists.

Solid condensation, or crystallization, represents the transition from a gas directly to a solid state, bypassing the intermediate liquid stage. This process often manifests itself under specific conditions, such as sublimation or intense and rapid cooling promoting solidification rapidity of molecules. The formation of solid crystals results from molecular reorganization from a gas structure, forming an ordered and regular arrangement in a crystal lattice. 

Crystallization conditions and examples

Crystallization can occur when atmospheric conditions favor sublimation, where the gas goes directly to the solid state. Examples include the formation of snow crystals from water vapor in the atmosphere or the sublimation of carbon dioxide(CO2) to form frost. Crystallization can also be caused by the rapid cooling of a gaseous substance, promoting rapid solidification of molecules.

An example of condensation is that of diode vapors which condense in the form of crystals on cold walls, without passing through the liquid state. Under normal temperature and temperature conditions pressure, the diode is in a solid state. But, when we heat diode pellets in a test tube, purple vapors are emitted. These are also toxic and irritating; all necessary precautions must be taken during the experiment. The part of the vapors which touches the top of the tube, which is colder, immediately transforms back into crystals, without passing through a liquid state. It is said that there is condensation of the diode vapors.