Author: Edgar Zhu
Editor: Peggy Yang, Michael Zhu
Artist: Nicole Wang
Summer is just around the corner, and there's nothing better than coming home from the sweltering heat, turning on the air conditioner, and pulling a popsicle out of the fridge. The cold of a popsicle quickly takes away the uncomfortable heat, but there's one thing you notice every time you eat a popsicle: the packaging of the popsicle is always covered with a layer of water droplets. Have you ever thought about the reasons behind it? Is it because the popsicle itself is “sweating” because it's so hot, or is there a leak in the fridge?
Most matter in the world has three states: solid, liquid, and gas. The interchange of the three forms involves six changes. The processes that include heat absorption and emission are: melting (solid to liquid), vaporization (liquid to gas), sublimation (solid to gas), solidification/freezing (liquid to solid), condensation (gas to liquid), and deposition (gas to solid). The sweating of popsicle packaging is the effect of condensation.
First of all, why do we want to eat a popsicle after going outside on a hot day? Because we feel uncomfortable in the hot weather outdoors, and popsicles are freezing cold when we take them out from the refrigerator. This temperature difference causes us to transfer some of our heat to the popsicles, thereby lowering our body temperature. So, where do some of this heat go? Our cold popsicle absorbs it. This is an endothermic process for a popsicle.
Similarly, when a popsicle is taken out of the refrigerator, the packaging of the popsicle has a very low temperature. In contrast, the water vapor in the outside air has a very high temperature. When the water vapor in the hot air encounters the cold packaging of the popsicle, it undergoes an exothermic process: the heat is transferred to the packaging of the popsicle. When water vapor is cooled, it begins to liquefy. The water vapor, attached to the popsicle packaging, changes from a gas to a liquid, turning from water vapor to a drop of water. So, your popsicle isn't sweating, and your fridge isn't leaking either. The water droplets on the packaging of popsicles come from water vapor in the air around it that sticks to it.
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