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Name: Kevin M.
Status: student
Age:  15
Location: N/A
Country: N/A
Date: 2000-2001


Question:
How does the rate of evaporation relate to temperature and attractive forces?


Replies:
Kevin,

Attractive forces between atoms, ions, and molecules weaken as temperature is increased because heating makes those particles vibrate and move faster. The greater their relative motion, the harder it is for them to hang on to each other. That's why water evaporates faster if you heat it.

Regards,
ProfHoff


RATES of evaporation are difficult to treat quantitatively, because the rate depends on many "outside" factors like: Is the evaporation by diffusion, by convection, or by transpiration? Qualitatively, one can say that the rate of evaporation would be proportional to the vapor pressure of the substance, which depends upon the temperature like: ln(p) = -(H/RT) + constant, where p is the vapor pressure, H is the heat of vaporization, R is the gas constant and T is the absolute temperature in kelvins. In general, the stronger the attractive forces between molecules, the greater H will be, but it is not possible to be very precise about the details.

Vince Calder


Evaporation has to do with liquid molecules (i.e., molecules that are jostling against each other) breaking away from a surface and going into the gas phase where they rarely hit another molecule.

The rate of evaporation is how fast molecules go from the liquid phase to the gas phase. Anything that makes it easier for the molecules to break away from each other will increase the rate of evaporation.

Does heating the liquid make it easier or harder for the molecules to break away from each other?

Do strong attractive forces make it easier or harder for the molecules to break away from each other?

Greg Bradburn


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