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Evaporation is a cooling process?

  1. Mar 25, 2006 #1
    A few days ago i took a test on heat and temperature ect. One of the questions was : When we say evaporation is a cooling process, we are saying that: a. surrounding air is cool b. the liquid is cooled. I chose a. because i knew that evaporation draws in energy from air to evaporate cooling the air. My support for this was that freezing releases energy warming air and melting also takes in air cooling it. At the same time i was wary that when a liquid evaporates it loses some energy from the escaping molecules that turn to gas. Anyways i would like to know what i did wrong and i have yet to have time to ask my teacher.
  2. jcsd
  3. Mar 25, 2006 #2
    Yes, you are right. Evaporation is the process whereby atoms or molecules in a liquid state gain sufficient energy to enter the gaseous state. Therefore it is an endothermic process. Moreover, gas has less order than liquid or solid matter, and thus the entropy of the system is increased, which always requires energy input. In your case, this energy input should come from the surrounding air, thus cooling it.
  4. Mar 25, 2006 #3
    thanks just making sure i at least understood what was going on
  5. Mar 27, 2006 #4
    Either of the options can be an answer. We have evaporative air coolers as well as evaporative water coolers (aka cooling towers).

    The most probable answer to the question will be 'water' (by the literal sense of the question as it is water that evaporates)
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