Evaporation

Examples of Evaporation in the following topics:

• Water’s Heat of Vaporization

  • Evaporation of water requires a substantial amount of energy due to the high heat of vaporization of water.
  • The fact that hydrogen bonds need to be broken for water to evaporate means that a substantial amount of energy is used in the process.
  • As the water evaporates, energy is taken up by the process, cooling the environment where the evaporation is taking place.
  • In many living organisms, including humans, the evaporation of sweat, which is 90 percent water, allows the organism to cool so that homeostasis of body temperature can be maintained.
  • (b) If the container is sealed, evaporation will continue until there is enough vapor density for the condensation rate to equal the evaporation rate.

• The Water (Hydrologic) Cycle

  • For example, when water evaporates, it takes up energy from its surroundings, cooling the environment.
  • The evaporation phase of the cycle purifies water, which then replenishes the land with fresh water.
  • This leads to the evaporation (water to water vapor) of liquid surface water and the sublimation (ice to water vapor) of frozen water, which deposits large amounts of water vapor into the atmosphere.
  • Rain eventually percolates into the ground, where it may evaporate again (if it is near the surface), flow beneath the surface, or be stored for long periods.
  • Water from the land and oceans enters the atmosphere by evaporation or sublimation, where it condenses into clouds and falls as rain or snow.

• Movement of Water and Minerals in the Xylem

  • Transpiration is the loss of water from the plant through evaporation at the leaf surface.
  • Transpiration is caused by the evaporation of water at the leaf, or atmosphere interface; it creates negative pressure (tension) equivalent to –2 MPa at the leaf surface.
  • The wet cell wall is exposed to the internal air space and the water on the surface of the cells evaporates into the air spaces.
  • Evaporation from the mesophyll cells produces a negative water potential gradient that causes water to move upwards from the roots through the xylem.

• Heat Conservation and Dissipation

  • For example, vasodilation brings more blood and heat to the body surface, facilitating radiation and evaporative heat loss, which helps to cool the body.
  • Some animals seek water to aid evaporation in cooling them, as seen with reptiles.

• Homeostasis: Thermoregulation

  • Heat can be exchanged between an animal and its environment through four mechanisms: radiation, evaporation, convection, and conduction.
  • When a mammal sweats, evaporation removes heat from a surface with a liquid.
  • Heat can be exchanged by four mechanisms: (a) radiation, (b) evaporation, (c) convection, or (d) conduction.

• Waxes

  • Plants also use waxes as a protective coating to control evaporation and hydration and to prevent them from drying out .

• Subtropical Deserts and Chaparral

  • In some years, evaporation exceeds precipitation in this very dry biome.
  • Finally, upwelling deserts exist adjacent to areas where cold currents rise to the ocean surface, reducing evaporation.

• Boreal Forests and Arctic Tundra

  • Little evaporation occurs because of the cold temperatures.
  • As in the boreal forests, there is little evaporation due to the cold temperatures.

• Inorganic Nutrients and Other Factors

  • Wind can be an important abiotic factor because it influences the rate of evaporation and transpiration.

• Water’s Cohesive and Adhesive Properties

  • This pull results from the tendency of water molecules being evaporated on the surface of the plant to stay connected to water molecules below them, and so they are pulled along.