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Evaporation Rate
Name: Amanda
Status: student
Age: 12
Location: N/A
Country: N/A
Date: Around 1999
Question:
If you have different kinds of liquids like vinegar,
alcohol, water, saltwater,juice and vegetable oil and you put one group
of them in the sun and another group in a cool dark place, why does the
alcohol evaporate the fastest in both places?
Also, where can I find more information on evaporation of different liquids?
Thank you for helping me!
Replies:
Hi Amanda... you are a good observer! Yes...different
liquids evaporate at different rates...Why?
see...the molecules of a liquid are in constant motion,
some moving fast, others slowly. Occasionally one of
these molecules (due to this movement) has enough
kinetic energy to escape from the liquid's surface
and become a molecule of vapor. If a liquid, or some
liquids, is placed in an open container, it will in
due time disappear through evaporation. The vaporized
molecules disperse throughout the atmosphere, and
eventually all the liquid molecules will escape as
they enter the vapor state.
To convert a liquid to a vapor it is need heat.A liquid evaporating at room
temperature absorbs heat from its
surroundings. The amount of heat required to vaporize
a given amount of liquid depends from the kind of
liquid, beeing characteristic of a given liquid. We
call molar heat of vaporization the quantity of heat
required to vaporize 1 mol of a liquid at a constant
pressure. For example the heats of vaporization of benzene,
methanol, ethanol, are lower than the one from the water,
and then they evaporate first . This happens also with
some of the liquids you mentioned...the oil has a quite
high heat of vaporization and practically will not
evaporate, unless you heat it.
But be careful, the heats of vaporization are constants
valid for pure substances, then in the case of salted
water, for example (that is a solution) the water will
evaporate leaving the dissolved salt as a solid.
You can find the values of these constants in a good
HandBook of Chemistry and Physics.
Thanks for asking NEWTON!
Mabel
(Dr. Mabel Rofrigues)
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Update: June 2012
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