Why Does Boiling Water Bubble?
When you boil water in a teakettle, you heat it to the point where it changes from a liquid to an invisible water gas called “steam.”
Bubbles of steam rise through the water and escape into the air. This bubbling is called “boiling.”
By the time the steam has gone an inch or so from the teakettle spout, the steam cools and partly condenses into a cloud of tiny water droplets, much like those your warm breath makes on a cold day.
If the water boils long enough, it will all turn to steam (or “water vapor” as it is often called) and disappear into the air.