Why Do Bubbles Form When Water Boils?

[Nerv68]

When something is boiling, like water on a stove, where do the bubbles come from? is it from some sort of chemical reaction?

 

[turbo]

If you are boiling water, you are heating it so that some of the water undergoes a phase change from liquid to vapor. There is no chemical reaction going on.

 

[russ_watters]

Ie, the bubbles are the boiling. And the reason they come up from the bottom is the heat is applied to the bottom of the container, so that's where the bubbles of vapor form.

 

[Astronuc]

Very small bubbles in water will initially be dissolved air coming out of solution and nucleating into bubbles, then as turbo and Russ indicated, the rest is liquid to steam transformation as the liquid reaches the boiling (saturation) point. As energy enters the liquid, the temperature will remain constant because the energy goes into a phase change (assuming the pressure remains constant).

Vapor bubbles will nucleate in the small imperfections in the surface of the pot/kettle.