What will happen if a partially inflated party balloon were heated?

Answer 1

The air molecules would expand, increasing the pressure of the balloon.

When anything gets cold, it contracts, and when heated, it expands.

Atoms and molecules are always moving - when something is hot, the molecules are moving faster and greater distances. When something is cold, the molecules are still moving, just slowly and at much smaller distances.

You won't see much a difference while it's partially inflated, though there would be one.

You can see results more drastically by heating a balloon that is near completely inflated.

The more air molecules that are in the balloon, the greater the expansion. In other words, the bigger the balloon and more air that's in it, when heated you will see a larger change in the balloon size.

Answer 2

Heating a partially inflated party balloon will cause the air inside to expand, increasing the pressure. If the balloon cannot expand to accommodate the increased pressure, it may burst.