why does water bubble when it boils?

Answer 1

because past the "boiling point" water starts a highly accelerated mode of turning from liquid state into gaseous state (water vapour, or steam) and as it travels from the bottom of the vessel where the heat source is, that spot of gaseous water is surrounded by water that is still liquid, so it forms a "bubble". The bubble of gaseous H2O (water vapour or steam) is lighter than the surrounding liquid H20 (water), so it rises up through the liquid H20 (water) until it reaches the surface at the top and releases and spreads out that gaseous H20 (water vapour or steam) into the air. That process is the bubbling action of boiling water.

Answer 2

There are two types of bubbling that ocurr when heating water to boil.

The first type is the creation of steam bubbles as water changes phase from a liquid into a gas.

The second type happens as the water is heated but before the water is boiling. You may see a fine layer of small bubbles form on the surface of the pot. These bubbles are actually gasses which were disolved in the water comming out of solution as the water is heated.


The temperature at which water will turn into steam depends on the pressure. Water at atmospheric pressure will boil at 212F/100C . If you raise the pressure more energy will be necesssary to boil water so the water will boil at a higher pressure.

Water has weight and the weight of water is added to the pressure. This means that the water at the bottom of the pot is under s;ightly more pressure. It is also where the heat is applied.

Once the water at the bottom of the pan starts to turn into steam it under goes a density change. Steam has a volume 350 times greater than the water volume from which it was boiled.

As a steam bubble is formed it rapidly rises in the water and expands creating a larger bubble of steam. Not only that but it was created in an area of the pot where a little more heat was necessary to generate teh steam bubble due to the added weight of the water. So as this small bubble rises and expands it is bringing water that is just ready to boil from the bottom of the pot to the surface where there is less pressure. This hotter water will also flash into steam when is reaches an area where the pressure will allow it to turn or flash into steam. So you may see some bubbles seem to form near the bottom but not at the bottom of the pot and this is why you may notice this effect.

Answer 3

Under the ocean near volcanic activity, the water gets 700 degrees without bubbling because the pressure of the ocean is so great that it can't bubble. Also, people have been known to boil water in a pyrex dish in the microwave, but the water doesn't bubble/boil although it is hot enough to. They pick the dish up and set it down on the counter, and it "explodes" and burns them. The pyrex glass is so smooth and without imperfections that it doesn't trigger the boiling action until the dish is jostled.

Answer 4

When you boil water the heat source is from the bottom. The water at the base of the pan heats up first and then this slowly heats up the water above it.

When the water gets to boil it is the water at the bottom that boils first, as it is the hottest. The water changes from a liquid to a gas. The gas then expands forming a bubble which rises up through the water above as it is less dense.

Answer 5

Boiling is a form of evaporation, and can be a gentle simmer or happen explosively. Any liquid can boil, not only water.
At ordinary low temperatures, water, left open to the air, gently evaporates from its surface. Its vapor exerts a pressure, which at such low temperatures is much less than the pressure of the surrounding atmosphere. The water also tries, through the formation of microscopic bubbles, to evaporate in its interior, but these tiny bubbles of water vapor, at the low pressure it would have at these low temperatures, are immediately suppressed by the much higher pressure of the atmosphere pressing down on the liquid's surface. But when the water is heated and its temperature reaches 212 degrees Fahrenheit, its vapor pressure reaches the pressure of the surrounding air, so the bubbles that form by evaporation in the interior of the liquid are no longer suppressed. They grow to large size, rise to the surface, and there release their vapor to the air. That sometimes explosive evaporation that starts in the interior of the liquid is boiling. The bubbles are water vapor, maybe mixed with a little air that had been dissolved in the water to start with. The tiny bubbles you see when you first start heating the water are mostly just previously dissolved air that is now coming out. That is not boiling.

At high altitudes the pressure of the atmosphere is less than at sea level, so the temperature needed to reach the boiling point is less than the 212 degrees it is at sea level. The water then boils at that lower temperature. In Denver, Colorado, a mile above sea level, the boiling point is far enough below 212 degrees that it takes 4 minutes to cook a "3-minute" egg !

If you dissolve salt in the water its vapor pressure is depressed so you then have to heat the water to a higher temperature to get it to boil. That is the opposite of the high-altitude effect. With a teaspoon of salt dissolved in a quart of water the boiling point is higher than that of pure water by between 1/3 and 2/5 of a degree Fahrenheit. That difference, although small, is easy to measure to high accuracy with a good laboratory thermometer. The good agreement between such measurements and the predictions of theory provided, in the late 19th and early 20th century, important confirmation of the atomic constitution of matter: that ordinary table salt, in this case, consists of electrically charged atoms ("ions") of sodium and chlorine that float apart from each other when dissolved in the water, each individual ion then making its contribution to the lowering of the vapor pressure and so to the raising of the boiling point.

Answer 6

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RE:
why does water bubble when it boils?

Answer 7

As sufficient energy is added to the water molecules at the bottom, they become steam [this is called a "phase transition"]. The steam, being far less dense than the liquid water, rises quickly to the top of the liquid, causing the "boiling" effect.

Answer 8

Increase in Kinetic Energy of the water molecules.

Answer 9

Those bubbles are hydrogen gases. Due to its high temperature, hydrogen gas becomes less soluble in water.

Answer 10

H2O(g) is being evolved from solution