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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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