Archives of Ask A Scientist!

About "Ask A Scientist!"

On September 17th, 1998 the Ithaca Journal ran its first "Ask A Scientist!" article in which Professor Neil Ashcroft , who was then the director of CCMR, answered the question "What is Jupiter made of?" Since then, we have received over 1,000 questions from students and adults from all over the world. Select questions are answered weekly and published in the Ithaca Journal and on our web site. "Ask A Scientist!" reaches more than 21,000 Central New York residents through the Ithaca Journal and countless others around the world throught the "Ask a Scientist!" web site.

Across disciplines and across the state, from Nobel Prize winning scientist David Lee to notable science education advocate Bill Nye, researchers and scientists have been called on to respond to these questions. For more than seven years, kids - and a few adults - have been submitting their queries to find out the answer to life's everyday questions.

Previous Week's Question Published: 18 July, 2001 Next Week's Question
Water not only liquid that evaporates
Question
Can only water evaporate or can other liquids?

Question
Evaporation, in which liquid at a surface is converted into vapor, can take place for all liquids, not just for water. A vapor is composed of molecules that have broken free from the surface of the liquid. From our everyday experience, we know that an uncovered glass of water left out on a countertop will eventually evaporate completely into water vapor. This is also true of other liquids, such as rubbing alcohol, gasoline, ammonia or oil.

Now suppose you took your glass of water from the countertop and sealed it inside a somewhat larger, airtight container. What do you think would happen? If you observe the process over a period of time, you will see the water level drop initially and then (if you started with enough water) evaporation will seem to stop. Your closed system has reached equilibrium: There is enough water vapor in the closed container that molecules are condensing back onto the surface at the same rate as they evaporate. The rate of evaporation is different for different liquids. For instance, alcohol evaporates more quickly than water, while oils takes much longer.

The rate of evaporation also depends on the temperature of the liquid and its surroundings. Some heavy oils (or exotic liquids like liquid mercury) may need to be heated before they show appreciable evaporation.

If you raise the temperature of a liquid enough you can start a process of evaporation within the liquid itself. This process is another very familiar one-it's called boiling!

Related Questions