Evaporation

Aerosol of microscopic water droplets suspended in the air above a cup of hot tea after the water vapor has sufficiently cooled and condensed. Water vapor is an invisible gas, but the clouds of condensed droplets refract and scatter the sunlight and are thus visible.
Droplets of water vapor in a pan.
Demonstration of evaporative cooling. When the sensor is dipped in ethanol and then taken out to evaporate, the instrument shows progressively lower temperature as the ethanol evaporates.
Rain evaporating after falling on hot pavement

Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase.[1] A high concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidity affects rate of evaporation of water.[2] When the molecules of the liquid collide, they transfer energy to each other based on how they collide. When a molecule near the surface absorbs enough energy to overcome the vapor pressure, it will escape and enter the surrounding air as a gas.[3] When evaporation occurs, the energy removed from the vaporized liquid will reduce the temperature of the liquid, resulting in evaporative cooling.[4]

On average, only a fraction of the molecules in a liquid have enough heat energy to escape from the liquid. The evaporation will continue until an equilibrium is reached when the evaporation of the liquid is equal to its condensation. In an enclosed environment, a liquid will evaporate until the surrounding air is saturated.

Evaporation is an essential part of the water cycle. The sun (solar energy) drives evaporation of water from oceans, lakes, moisture in the soil, and other sources of water. In hydrology, evaporation and transpiration (which involves evaporation within plant stomata) are collectively termed evapotranspiration. Evaporation of water occurs when the surface of the liquid is exposed, allowing molecules to escape and form water vapor; this vapor can then rise up and form clouds. With sufficient energy, the liquid will turn into vapor.

  1. ^ "the definition of evaporate". Dictionary.com. Retrieved 2018-01-23.
  2. ^ "Why Does Humidity & Wind Speed Affect Evaporation?". Sciencing. Retrieved 2022-08-20.
  3. ^ "Evaporation". The New Student's Reference Work (1914). 1914. p. 636.
  4. ^ Lohner, Science Buddies, Svenja. "Chilling Science: Evaporative Cooling with Liquids". Scientific American. Retrieved 2018-01-23.{{cite news}}: CS1 maint: multiple names: authors list (link)