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Size-Changing Science: How Gases Contract and Expand

A chemistry challenge from Science Buddies
 
Observations and results
Did balloon number 1, which was placed in the freezer, shrink a little compared with balloon number 2, which stayed at room temperature?
 
You should have seen that when you put the balloon in the freezer, the distance between the lines decreased a little, from about two and a half inches to two and a quarter (or by a quarter inch, about 10 percent). The balloon shrank! The distance between the lines on the balloon kept at room temperature should have pretty much stayed the same (or decreased very slightly), meaning that the balloon shouldn’t have really changed size. The frozen balloon shrank because the average kinetic energy of the gas molecules in a balloon decreases when the temperature decreases. This makes the molecules move more slowly and have less frequent and weaker collisions with the inside wall of the balloon, which causes the balloon to shrink a little. But if you let the frozen balloon warm up, you would find that it gets bigger again, as big as the balloon that you left at room temperature the whole time. This is because the average kinetic energy would increase due to the warmer temperature, making the molecules move faster and hit the inside of the balloon harder and more frequently again.
 
More to explore
Looking for a Gas, from Rader’s Chem4Kids.com
Gases around Us, from BBC
Balloon Morphing: How Gases Contract and Expand, from Science Buddies
Racing to Win That Checkered Flag: How Do Gases Help?, from Science Buddies

This activity brought to you in partnership with Science Buddies

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