how can we explain evaporation (to get 5marks)

Asked by satjorabazar | 12th Sep, 2015, 09:31: PM

Expert Answer:

  • It is the process in which atoms or molecules in a liquid state gain sufficient energy to enter the gaseous state.
  • It is the opposite process of condensation.
  • The thermal motion of a molecule of liquid must be sufficient to overcome the surface tension and evaporate, that is, its kinetic energy must exceed the cohesion forcess at the surface.
  • Hence, evaporation proceeds more quickly at higher temperature, at higher flow rates between the gaseous and liquid phase and in liquids with lower surface tension (i.e. higher vapor pressure).
  • As only a small proportion of the molecules are located near the surface and are moving in the proper direction to escape at any given instant, the rate of evaporation is limited.
  • Also, since the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid thus decreases.
  • This phenomenon is called as evaporative cooling.
  • This is the reason why evaporating sweat cools the human body.

Evaporation can be shown using following diagram:

 
 

Answered by Prachi Sawant | 13th Sep, 2015, 01:30: PM