Observations and results
Were you able to see the effect of evaporation on the chocolate candies? Did the candy wrapped in the wet paper towel show fewer signs of melting than the one wrapped in the dry towel?
Just as sweating cools you on a hot day, when water is evaporated from the wet paper towel strip, it keeps the chocolate candy cooler compared with the candy wrapped in a dry towel. When the lightbulb heats the water on the wet strip, the liquid evaporates and turns into a gas, called water vapor. This vapor carries heat away, removing it from the area surrounding the candy, and keeps the candy cooler than it would be if there were no water to evaporate. This will probably not completely prevent the candy from melting but, overall, it should be visibly obvious that the candy in the wet paper towel strip melted less than the candy in the dry strip.
If you tried fanning the chocolate candies while they were under the lamp, the breeze should have helped to increase the rate of evaporation. Because water vapor is less dense than dry air, it tends to stay around the object it evaporated from, making the surrounding air more and more humid and thereby difficult for additional evaporation to continue over time, because it has nowhere to go. The wind disperses the existing water vapor, making room for more water vapor to be made, which allows more evaporation—and thus cooling—to take place. Putting additional water on your skin or an object can also help increase the evaporation rate, which is why some people put wet bandanas around their necks when exercising.
Cleanup
Because chocolate can stain, be careful not get any melted chocolate on your clothes or furniture before discarding it and the candy wrappers.
More to explore
"Digit's B-Day Surprise," CYBERCHASE from Thirteen/WNET, Educational Broadcasting Corporation, New York
The Water Cycle: Evaporation, from USGS
"What's Sweat?" from KidsHealth
"Keep Your Candy Cool with the Power of Evaporation!" from Science Buddies
This activity brought to you in partnership with Science Buddies and Cyberchase
Subscription Center
See what we're tweeting about
4 Comments
Add Comment"Discard" the candy? I have a better idea. A very good experiment.
Reply | Report Abuse | Link to thisThe experiment naturally raises the question "Just what is it about evaporation that cools the candy (or your skin, etc.) in the first place?" That is, why does it carry heat away?
Reply | Report Abuse | Link to thisWhen the water molecules absorb heat energy, they disperse and transfer their excess energy to the surrounding air. But since the dry candy wrapper doesn't evaporate when it heats up, it transfers most of its heat energy to the candy instead.
Reply | Report Abuse | Link to thisI would tend to think that putting a chocolate bar in a wet paper towel would be a bad way to preserve it regardless of how well it cools it...
Reply | Report Abuse | Link to this