Why Do Bubbles Form When Water Boils?

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    Boiling Bubbles
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SUMMARY

Bubbles form when water boils due to the phase change from liquid to vapor, not from a chemical reaction. The bubbles originate from the bottom of the container where heat is applied, causing vapor to form. Initially, small bubbles consist of dissolved air escaping from the water, while larger bubbles result from the transformation of liquid to steam as the water reaches its boiling point. Vapor bubbles nucleate at imperfections on the surface of the pot or kettle.

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  • Understanding of phase changes in matter
  • Basic knowledge of thermodynamics
  • Familiarity with boiling point concepts
  • Awareness of nucleation processes in liquids
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  • Explore the concept of nucleation in boiling liquids
  • Study the effects of pressure on boiling points
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Students in chemistry or physics, educators teaching thermodynamics, and anyone interested in the science of boiling and phase changes.

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

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