Evaporation

[Rockazella]

I know it's the kinetic energy (temp.) of the molecules that controls evaporation. Just wondering what causes some liquids to evaporate more quickly than others at the same room temp... for example gasoline?

[On Radioactive Waves]

It depends on how much heat it takes to make the transition. A higher specific heat means more energy required to reach the same temperature. The temperature at which they make a phase change can be different. The enrgy required to make the phase change also varies.

[Integral]

Another key factor is surface tension, gas has a very low surface tension, this allows molecules to escape the fluid at a lower velocity, thus lower liquid temperature.

[Rockazella]

Alright those make sense, thanks.

I have a follow up question that's slightly off topic of the first:

When I posted the first question I was under the impression that phase change was due to greater kinetic energy of the molecules. However, since posting it I've done a bit of reading online. The site I read said that phase change occurs because of an increase in potential energy of the molecules. It explains the potential energy of molecules as the average distance between them, greater distance= greater potential energy. I must say, I dont understand this. Seems to me that a greater average distance will be the result of higher velocity or more kinetic energy. Can anyone help me to make sense of this molecular potential energy concept?

[pop676]

itim not an expert so im not goin to attempt to make a feeble explanation but it has to do with the electrons phase shifting or juming from one energy level to another

[HallsofIvy]

Pop676: "electrons phase shifting or juming from one energy level to another" produces light. I don't see what that has to do with evaporation.

I believe that it is true that liquids consisting of less massive molecules evaporate more quickly.

[kishtik]

I will try to answer but I want you to know that I'm not an expert too.

First of all the gravitational potential energy (there are others) depends on the distance between the molecules, like it does between you and the Earth. The higher distance is the higher potential energy you have. Maybe they meant distance by saying 'potential energy'. Can I be right?

Best wishes

[Rockazella]

Kish,
yes you could be right, but my question is what's maintaining that greater distance AND what would cause the molecules to all of a sudden go farther apart? Like I said before, it seems to me that only a greater kinetic energy would do this(a molecule with more velovity would be able to get farher away from another molecule before it turns back). Yet, what I read says when phase change ocures the kinetic energy practically stays the same, but the potential increases. Not to be repetative, but I'm not understand how a molecules PE can go up without it be caused by a greater KE.

[kishtik]

Originally posted by Rockazella

how a molecules PE can go up without it be caused by a greater KE.

I have no idea...[:(]

[zoobyshoe]

Rockazella,

Could you post the original
paragraph explaining that, verba-
tim? Or a link? That is very con-
fusing to me as well.

-zoob


Also, here is a link to an article
that goes into detail about your
first question, and explains it
pretty well:

vapor pressure (Chemistry, General) - 1Up Info - Encyclopedia
Address:http://www.1upinfo.com/encyclopedia/V/vaporpre.html

[TonyG]

As I've always understood it, it's the kinetic energy that's important. The molecules in the liquid are bouncing around, and once in a while, one will have enough speed/kinetic energy to break through the surface and escape into atmosphere above.

Perhaps a high PE is important because it can be converted to high KE -hence giving the liquid molecule a chance to escape.