albertlee Posted October 30, 2005 Share Posted October 30, 2005 I always wonder why this happens... if I place a cup of water on the table, after a very long time, the water is gone... why's that? why doesn't it remain liquid water? Link to comment Share on other sites More sharing options...
ecoli Posted October 30, 2005 Share Posted October 30, 2005 because there is energy in the air. It takes 1 cal. of energy to evaporate 1 gram of water. If you're not adding heat, then it takes longer to evaporate, energy is being transfered much slower. Link to comment Share on other sites More sharing options...
albertlee Posted October 30, 2005 Author Share Posted October 30, 2005 ????!! then why we call 100c the evaporating point? since even room temperature can evaporate as you say.... Link to comment Share on other sites More sharing options...
Keano Posted October 30, 2005 Share Posted October 30, 2005 100c is the boiling point not the evaperating point Link to comment Share on other sites More sharing options...
ecoli Posted October 30, 2005 Share Posted October 30, 2005 ????!! then why we call 100c the evaporating point? since even room temperature can evaporate as you say.... it's the boiling point... look at the link http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/phase.html Link to comment Share on other sites More sharing options...
albertlee Posted October 30, 2005 Author Share Posted October 30, 2005 well,. boiling point indicates the amount of heat to change water from liquid into gas... I think evaporating is the same.... any help here? Link to comment Share on other sites More sharing options...
jdurg Posted October 30, 2005 Share Posted October 30, 2005 Nope. The boiling point is the temperature at which the vapor pressure of the liquid is equal to the atmospheric pressure. Link to comment Share on other sites More sharing options...
albertlee Posted October 30, 2005 Author Share Posted October 30, 2005 this is abit confusing... if water is evaporated in room temp, then, its pressure does not equal to the ATM? Link to comment Share on other sites More sharing options...
Borek Posted October 30, 2005 Share Posted October 30, 2005 At room temperature vapor pressure is much lower than atmospheric presuure, thus the liquid (call it water ) evaporates only on the surface. Once the liquid is heated to the boiling temperature, it can evaporate not only on the surface, but also inside of its volume, That's the difference between evaporating and boiling. Best, Borek -- Chemical calculators at www.chembuddy.com pH calculator concentration conversion Link to comment Share on other sites More sharing options...
albertlee Posted October 31, 2005 Author Share Posted October 31, 2005 thanks Borek.... Link to comment Share on other sites More sharing options...
swansont Posted October 31, 2005 Share Posted October 31, 2005 The molecules have a distribution of energies. Some fraction will have enough to escape; this lowers the average energy of the remaining molecules, which is why evaporation is a cooling process. Link to comment Share on other sites More sharing options...
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