What happened as the balloon was heated? Heat from the candle transferred into the balloon rubber and whatever was filling up the balloon...this is known as thermal conduction. When you heat a gas or liquid, it expands and rises up. Why is this so? The density of the gas (air) or liquid (water) decreases as it heats up.
Why did the air-filled balloon pop? The air filled balloon pops because the air quickly expands and does not absorb enough of the thermal energy from the rubber to protect the balloon. This added energy causes the molecules in the rubber of the balloon to spread apart. As a result the balloon partially melts or burns, then quickly bursts, unable to withstand the added pressure of the enclosed air.
The water filled balloon, on the other hand, does not burst because the rubber obviously does not reach a temperature sufficient for it to melt or burn. Water is a great substance for soaking up heat. The thin balloon allows the heat to pass through very quickly and warm the water through a process called thermal conduction. Thermal conduction is the ability of a medium to allow heat to be conducted through it. The heat will always travels from a hotter spot to a cooler spot. In this case, the cooler water absorbs the heat from the candle and rises, drawing the heat away from the balloon rubber so that the balloon survives the flame. Once the hot water rises away from the flame to the top of the balloon, it cools down, dropping back towards the flame to then get hot and rise again This process is continual convection current, whereby the warming water rises and the cooling water falls. This process helps to keep the balloon from popping by constantly drawing heat away.
Using water to control heat is a valuable process. In fact, firefighters in Colorado often use a polymer foam to control large wildfires. Since polymers soak up a tremendous amount of water, they are useful in controlling and stopping the heat energy in the fire.
Your body even uses water to control heat. When you exercise, what’s that dripping from your armpits? E it’s sweat! But your body actually uses the water in your sweat to control your internal temperature so you don’t get overheated.