Why do pots boil over?

Answer 1

I think this is an excellent question especially in light of all of the WRONG answers given. Several people have suggested that the heat from the stove heats up dissolved AIR in the water. Or, the heat disassociates the molecular structure of water and separates oxygen from the hydrogen and the resultant gases erupt from the water. Thats a good one-I wish just boiling water disassociated the oxygen from the hydrogen! If that were the case we wouldn't be spending $4 per gallon of gas. We would be boiling water and putting the hydrogen in our cars. But I diverge. Heating the water brings the water to above its boiling point which is 212 F at sea level. The water flashes, It changes from the liquid phase to the gaseous phase and those are the bubbles that come to the top. Water in gas phase. No air bioling over, No oxygen, No hydrogen, no nitrogen. Just pure water in gaseous form, otherwise known as steam

Answer 2

Or because they are potboilers.

Pots only boil if they contain a liquid and are heated. They are said to "boil over" if they are covered and the liquid escapes from the lid, flowing down the side of the pot.

Liquids boil because they a) contain air dissolved in the liquid or b) are vaporized by the heat or c) both of the above. This causes the liquid to expand and form bubbles. If the pot is covered, the bubbles will fill the space inside the pot and the bubbles create enough pressure to push the lid up. The bubbles push out from under the lid and burst, leaving a small amount of liquid and whatever was in the liquid to drip down the side of the pot. Removing the lid reduces the pressure inside the pot and the bubbles fall apart and drop back into the boiling liquid.

Answer 3

The real question here is, why do UNWATCHED pots boil over, because a pot will not boil over if you watch it and turn down the heat when it boils. The maxim that a watched pot never boils is of course not true. It only SEEMS that way. That is simply the time dilation effect of special relativity at work.

An unwatched pot boils over because it is seeking the attention you failed to give it by watching it during its formative warm-up period. Some recommend immediately rushing to reduce the heat, others say that rewarding this attention-seeking behavior will only cause it to be reinforced in the future.

Since doing nothing just makes a mess of the stove, I recommend putting a lid on it and taking it off the heat, to let it know that there are undesireable consequences to this attention-seeking behavior. It's never too late to start effective discipline!

Answer 4

Because boiling means water is being converted into steam. Boiling water contains steam bubbles each which take up about 1000 times as much volume as the same amount of water. As you can see if you get enough of these bubbles suspended in the liquid the pot could boil over.

Answer 5

Not every pot will boil over - if it is just plain water, there is nothing to make the water bubble and boil over. However, if you're boiling something like pasta, the starch in the pasta dissolves in the water, causing bubbles. You can avoid this by using a larger pot, with lower water level, and a lower temperature. The ideal scenario for avoiding this situation is water level at about half of the pot, and medium temperature on the burner.

Answer 6

The lid keeps the steam in until the pressure gets high enough. A pot with no lid usually doean't boil over unless it is filled close to the top.

Answer 7

Because the alternative is for them to boil under and that has never been observed.

Thus the old saying: "An observed pot never boils under."

Answer 8

Aside from the first answer, which is technically correct, the answer you are looking for is this. Cold contracts, heat expands. So when higher and higher temps. reach water, milk, whatever, the molecules expand, eventually so rapid is the expansion that it starts boiling, but the non boiling, yet still scalding water is still expanding in the pot. Eventually it is so hot and expanding so rapidly the container can no longer hold it all in and it flows over.

Answer 9

My comic answer is because someone used too much heat.

Reality answer, When a liquid is heated, from the bottom of the pan, you will see bubbles rising almost as if they are coming out of the bottom of the pan.

In actuality, this is a process of heat breaking down the molecular structure of H2O, (Water) and turning it into air bubbles(Oxygen) and if the heat is high enough, the bubbles become light and rise and when they all try and get out at the same time, the oxygen causes the remaining H2O (Water) to be forced out of the pan as well, because of over crowded conditions.

Good question,

Darryl S.

Answer 10

When it gets hot enough you start forming vapor bubbles faster than they can disipate. Since water vapor takes up more space than liquid water the actual water level in the pot goes up. Eventually it "boils over."