Why Do Bubbles Form When Water Boils?

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    Boiling Bubbles
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Discussion Overview

The discussion centers on the formation of bubbles when water boils, exploring the underlying mechanisms and processes involved. It addresses the phase change from liquid to vapor and the role of dissolved gases, as well as the physical conditions that facilitate boiling.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions whether the bubbles formed during boiling are a result of a chemical reaction.
  • Another participant clarifies that boiling involves a phase change from liquid to vapor without any chemical reaction occurring.
  • A participant explains that bubbles form at the bottom of the container where heat is applied, indicating that this is where vapor formation initiates.
  • It is noted that very small bubbles may initially consist of dissolved air coming out of solution, and that as the water reaches the boiling point, the transformation from liquid to steam occurs, with energy input causing a phase change while maintaining constant temperature.
  • Vapor bubbles are said to nucleate in small imperfections on the surface of the pot or kettle.

Areas of Agreement / Disagreement

Participants generally agree on the mechanisms of bubble formation during boiling, specifically regarding the phase change and the role of heat. However, there are nuances regarding the initial formation of small bubbles and the presence of dissolved gases that remain somewhat open to interpretation.

Contextual Notes

The discussion does not resolve the specifics of how dissolved gases contribute to bubble formation, nor does it clarify the exact conditions under which nucleation occurs in relation to surface imperfections.

Nerv68
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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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