Evaporating

Evaporating is the process by which a liquid changes into a gaseous state at the surface, typically occurring below the liquid’s boiling point. It happens when molecules at the surface gain enough kinetic energy to overcome intermolecular forces and escape into the surrounding air. Evaporation reduces the liquid’s mass and can happen at any temperature, not just at a boil.

Rate is influenced by temperature, surface area, airflow, and humidity. Higher temperatures increase molecular energy; a larger surface area exposes more molecules to escape; faster air movement removes vapor, lowering the local vapor pressure and allowing more evaporation; lower ambient humidity increases the driving force for vaporization. Evaporation stops only when the vapor pressure of the liquid equals the partial pressure of its vapor in the air, or when the liquid is exhausted.

Energy is required for vaporization, known as latent heat of vaporization. As molecules leave the liquid, the remaining liquid often cools. This evaporative cooling is common in nature and technology, such as sweating in animals or cooling towers in industry.

Evaporation is central to the water cycle and many practical processes. It dries wet surfaces, concentrates solutions, and enables desalination and distillation. In everyday life, evaporation explains why clothes dry after washing and why puddles shrink on sunny days.

Quantitative treatment uses mass transfer concepts; the rate is roughly proportional to surface area, temperature difference, and vapor pressure deficit between the liquid and surrounding air.