Why does boiling water bubble?
In: Chemistry
Well when water turns to a gas it’s a lot easier for it to happen at tiny imperfections such as dirt or chips in a container. (Called nucleation sites). Steam starts to form tat these jaggy edges in a bubble until it’s large enough to unstick itself. As it floats up and disturbs the rest of the hot water more steam is formed and the bubble collects more steam and gets bigger till it pops.
A super interesting and actually really dangerous thing happens if you heat filtered water in a clean cup in a microwave. The water can get hotter than the boiling point but without any jaggy edges or dirt bubbles can’t start to form. That gives you superheated water. Eventually the water will evaporate if kept hot and not bumped as steam can still form at the surface. But then as soon as you bump it the entire thing boils up at once and causes a tiny steam and hot water explosion. A bunch of people get hurt like this.
Its also the same principle behind why bonking a fresh beer bottle on top can cause the whole thing to foam over at once.
You have heard that water boils over a certain temperature. That is 100 deg Celsius. Water that is hotter is not liquid, but steam.
If you want to boil water, you put it into a pot and on the oven. That means the water is getting hot from below. Now the water that is touching the ground in the pot gets very hot, and part of it becomes steam. This steam rises to the top in a bubble. Now if the water is very cold, the bubble cools down fast enough , so that it does not reach the top. It only heats up the rest of the water. If the water is hot enough, this bubble will rise up to the top. And you have the strong bubbling you mentioned 😊
The boiling point of water is where water becomes steam.
As you boil water the water closest to the heating element becomes steam and forms bubbles which rise to the surface and pop becoming water vapor.
If you boil water long enough all the water in the container will eventually convert to steam in this way.
Well, by definition it’s not boiling unless it it’s forming bubbles! 🙂
But a less jokey response: why doesn’t water just spread out by itself and take up the whole room *normally*? It’s not just gravity – water can keep its shape in space just fine, as long as it’s under pressure. The reason is that it’s denser than air (which keeps it where it is) and under pressure (which stops it from spreading out).
Contrary to popular belief, liquids are turning to vapor all the time, even well below their boiling point. That’s why a small wet spot will dry up in an hour or two. Boiling is a different process, when this evaporation creates a gas with so much pressure that it’s able to overcome atmospheric pressure. In other words, the vapor inside the bubbles in boiling water pushes outward harder than the pressure from the air outside pushes inward, which lets the bubbles expand until the pressure falls to the point that these two forces cancel each other out.
Generally, it’s because when you are boiling water, the heating element and nucleation points are submerged. The bottom of a pan or cup for instance. This is where the heat contacting the water is hottest and where liquid water has a point to phase change to a gas. The now submerged gas is less dense than water, forms a bubble, and rises to the top.
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