Where do the air bubbles on the bottom come from when you boil water?
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It’s not air, it’s actually water vapour. When water boils, it turns from liquid water to gas water, but still just water.
Some of the bubbles may be from dissolved gases coming out of solution as the water warms (warm water can’t hold as much dissolved gas as cold water), but the big bubbles of boiling water is just water vapour.
It’s steam, also called water vapor (water in gas form). Think of heat as energy. Ice is water at low energy. The atoms that make up water slow down when they are cold, because they lose energy. They slow down so much that they (almost) freeze in place, forming a solid (ice).
Boiling water is the opposite. You are heating up the water, so the atoms are gaining energy and moving more. They move so much that they start bouncing around and rising into the air in the form of a gas. The gas (steam) is just water with a bunch of energy.
So in terms of energy (or heat) for water, solids (ice) have the lowest energy, liquids (water) are in the middle, and gases (steam/water vapor) have the highest energy.
boiling is a bulk phenomenon so the water on the lowest surface first heats up, due to it the water starts to expand turning water into water vapor then as the density of the water is higher than the water vapor so the vapor moves above the surface of the liquid water
water vapor (steam) is more energetic (heat) and could cause more damage to your skin than a boiling water
(it doesn’t happen when evaporate cause it is a surface phenomenon the water only on surface will turn into water vapor)
At first the bubbles are air that has dissolved in the water. Hot water isn’t as good at dissolving air so heating the water drives the air out, forming air bubbles on the edge of the container. Once the water is fully boiling, the bubbles are not of air but of steam, which is to say water vapour.
The reasons it looks like they’re coming from the bottom is because usually that’s the hottest point, that’s where the boiling is actually happening.
The small bubbles that appear on the bottom *before* the water starts boiling are air bubbles from air that was dissolved in the water. As the water heats up, it can hold less air, and the air exits the solution
Nucleation points. Nodes where what everyone else is describing is possible to form. The surface texture and shape of the container is what’s causing it. Pour (the same) beer (or Sprite) in a few different style glasses and see what happens.
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