2nd Class Power Engineering (2A1) Complete Exam Prep 2026

The process referred to as "evaporation" is accurately described by the transformation of a liquid into vapor when it occurs below the liquid's boiling point. This phenomenon can happen at any temperature, unlike boiling, which requires the liquid to reach a specific temperature where it changes to vapor throughout the liquid and forms bubbles.

During evaporation, molecules at the surface of the liquid gain enough energy to overcome intermolecular forces and escape into the air as vapor. This process is essential in various natural as well as industrial applications, such as cooling mechanisms (like sweating), humidity control, and concentration processes in chemical engineering.

The other options describe related but different concepts. The change of state from gas to liquid describes condensation, while the release of heat is more indicative of exothermic reactions or cooling processes. The cooling of a substance can occur as a result of evaporation, as it requires energy, which is drawn from the remaining liquid, leading to a drop in temperature.