ChemixaLEARN CHEMISTRY

Balloon gas laws

Objective: demonstrate Charles's law by heating and cooling a balloon, and Boyle's law by squeezing it. You will observe volume changes, connect them to particle motion, and explain both laws.

Safety:

Use warm tap water only, never boiling water. Do not overinflate balloons; they can pop loudly and startle. Keep balloons away from small children because of choking hazard. Adult supervision is required for minors.

Materials

  • Two balloons
  • Large bowl of warm (not hot) tap water
  • Large bowl of cold water with ice
  • Towel
  • Marker for measuring

Procedure

1

Inflate and mark

Inflate two balloons to a medium size, tie them off, and mark a line around the widest part of each with the marker.

2

Warm the balloon

Submerge one balloon in warm tap water for two minutes and observe the mark.

3

Chill the balloon

Move the same balloon into the ice water for two minutes and watch it shrink.

4

Confirm reversibility

Return it to room temperature and confirm it goes back to its marked size.

5

Squeeze for Boyle's law

Take the second balloon and gently squeeze one end, watching the other end bulge.

What to observe

  • The balloon visibly inflates in warm water and shrivels in cold water.

  • The size change reverses when the balloon returns to room temperature.

  • Squeezing one end makes the other end bulge outward.

  • Releasing the squeeze restores the original shape.

Why it happens

A balloon is a flexible container that keeps pressure nearly constant while its volume changes freely. Warming the air inside makes its molecules move faster and hit the balloon skin harder, so the balloon expands to keep the pressure balanced: volume is directly proportional to absolute temperature (Charles's law, V1/T1 = V2/T2). Cooling reverses the effect and the balloon shrivels. Squeezing the balloon demonstrates Boyle's law: at constant temperature, shrinking the volume raises the pressure, which you feel pushing back against your hands (P1V1 = P2V2). The balloon never touches extreme temperatures, so the air stays safely inside its elastic limits.

Try variations

  • Measure the circumference with a string before and after warming.

  • Chill the balloon longer and check whether it keeps shrinking.

  • Predict what happens in warm water versus hot tap water and discuss limits.