Expanding Hot Air

See how expanding hot air impacts the size of a balloon. Try this science experiment for kids to learn more about expanding gases, including carbon dioxide.

What You'll Need:

  • Bottle
  • Pan
  • Hot water
  • Balloon
  • Baking soda
  • Vinegar

Experiment 1: Hot Air

Step 1: Stretch the end of a balloon over the top of a bottle.

Step 2: Set the bottle in a pan of hot water.

After a few minutes, the heat will cause the air in the balloon to expand, making the balloon begin to blow up. This happens because the hot water heats up the air inside the bottle. The warmed air expands, filling up more space inside the balloon.

Experiment 2: Carbon Dioxide GasYou can also inflate a balloon slightly by making carbon dioxide gas.

Step 1: Put a cupful of water into an empty soda bottle.

Step 2: Add a spoonful of baking soda.

Step 3: Pour in a little bit of vinegar, and quickly put a balloon over the bottle top. You can tell carbon dioxide has been created when you see the balloon expand slightly.

Have you ever wondered how rain forms in the sky? Go to the next page to make a little rain indoors in a jar and find out more about it.

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