When a balloon (filled with air, for instance) is placed near a fire, the little particles of air inside of the balloon hit one another more and at faster speeds. The fast movement of these particles results in more pressure on the balloon from the inside. If the movements of the particles become fast enough, the balloon will not be strong enough to withstand the total pressure, and it will break at its weakest point.

Temperature is a measure of how fast the gas particles inside the balloon are moving. When the balloon is put near the fire, the temperature increases and the gas particles move faster and faster. As a result, they hit the inside walls of the balloon much harder and this causes the balloon to want to expand. Because of this, if the balloon expands too much, it will burst.

Two reasons: (1) rubber burns, so the fire weakens the part of the balloon close to the fire so that it can no longer hold, and (2) air inside of the balloon heats up to where the rubber can no longer hold it.

What happens if you put a balloon in the refrigerator? In the freezer? What happens to air when it gets hot? When it gets cold? Does this give you any ideas about how to answer your question?

The air in the balloon moves faster and faster when it gets hotter, and the fast-moving air molecules push each other farther apart, and the fast-moving air molecules push on the balloon to make it stretch. The balloon is stretchy. An empty plastic water bottle isn't very stretchy, so it would behave somewhat differently.