what does superheated water mean ?

Question

chemistry

Answer 1

Under the right circumstances, water can heat up above its boiling point without turning to gas. Then, when disturbed, the unstable equilibrium is broken, and the water boils explosively. Water can also be supercooled, where it falls below freezing point and then freezes spontaneously around a seed crystal.

Answer 2

It's water than has a temperature of more than 100 degrees Celsius at one atmosphere pressure yet doesn't boil because there happened to be no "seeds" (impurities, air bubbles) around which vapor bubbles could form. To make this you have to be very careful, the slightest shaking will create an air bobble which will act as a seed for a vapor bubble, and the upward drift of the vapor bubble will cause new ait bubbles to form etc.

Answer 3

It is water that is above it's boiling point, but has not boiled. This can occur if there is no site for nucleation to occur. Be carefull around superheated water, if you accidentally give it a nucleation site, it will all boil at once, and could give you a nasty scold.

Answer 4

superheated water is the one which is heated above its boiling point. by changing the pressure conditions.

Answer 5

Water boiled under pressure will boil at much hotter than normal.
Did you know that some metals will burn hot enough to actually separate the hydrogen from the oxygen and intensify the fire even more?

Answer 6

Water heated under pressure. It will stay in a liquid form well over the normal sea level boiling point. By the way, did you know that water will boil in a vacuum?

Answer 7

water heated past boiling point normally trapped under cooler substance. when give a chance to the energy is released explosively (no there's no fire)

Answer 8

its like if you put a cup of plain water in the microwave (and cook it for awhile)
it wont start boiling but once you put something in the water, it explodes
dont know why but its mad cool
be careful though cuz it hurts

Answer 9

WHAT IS SUPERHEATED WATER?

The term superheated water refers to liquid water under pressure between 100°C and its critical temperature, 374°C.
It is much less polar than water at ambient temperatures and can dissolve organic compounds, particularly if they are polarisable or slightly polar.
It can therefore be used as an alternative to organic solvents for environmentally friendly processes, avoiding residues in the products.
Extraction, liquid fractionation, chromatography, decontamination and flavour formation can be carried out.

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INTRODUCTION TO SUPERHEATED WATER

The term superheated water (alternatively subcritical water) refers to liquid water under pressure between 100°C and its critical temperature, 374°C. At lower temperatures and for most of this temperature range, the pressure of the medium does not have much effect on its properties, provided it is high enough to maintain the water in the liquid phase. Up near the critical temperature, the medium is very compressible and it has some of the properties of a supercritical fluid, and so the pressure does become important.



The relative permittivity (dielectric constant) of liquid water along the saturation line

Water changes dramatically when its temperature rises, because of the breakdown in its structure with temperature. The high degree of association in the liquid causes its dielectric constant (permittivity relative to vacuum) to be high at around 80 under ambient conditions, but as the temperature rises this falls, as is shown in the figure above. This figure gives values for liquid water along the saturation line, i.e. with just sufficient pressure to maintain it as a liquid. By 210°C its dielectric constant is equal to that for methanol (i.e. 33) at 25°C. At lower temperatures, superheated water has the polarity of methanol-water mixtures.

As a consequence, superheated water can be a good solvent for larger organic compounds, particularly if they have some polar groups or are polarisable like aromatic compounds. The solubility of an organic compound in superheated water is often many orders of magnitude higher than its solubility in water at ambient temperature for two reasons. The first of these is the change in dielectric constant, described above. The second is that solubilities typically increase with temperature, particularly a compound with low solubility at ambient temperature, which will have a high positive enthalpy of solution.

It has been shown experimentally that naphthalene forms a 10 mass % solution in water at 270°C and that both benz[e]pyrene and nonadecylbenzene reach the same concentration at 350°C. As an example the variation in the solubility of the pesticide chloranthonil is shown in the table below.

The solubility of chloranthonil in water

T/K mole fraction

323 5.41 x 10-8
373 1.8 x 10-6
423 6.43 x 10-5
473 1.58 x 10-3

Consequently superheated water can be used to process organic compounds in various ways as an alternative to using organic solvents. This has environmental and work-pollution advantages and avoids organic residues in products. It can be used to extract contaminants, such as polynuclear hydrocarbons and polychlorinated biphenyls from soil and sediment and essential oils or valuable compounds from plant materials. It can also be used to separate valuable perfume and flavour compounds from essential oils and also aromatic compounds can be extracted from petroleum products. Subcritical water has also been used for reverse-phase chromatography: water up to 210°C was used with a polymer stationary phase to separate a wide variety of compounds and gave chromatograms comparable to those obtained with solvent mixtures at ambient conditions.

Reactions and reactions combined with extraction can also be carried out. In so-called wet oxidation processes, superheated water and air or oxygen are used to dispose of toxic waste materials. Explosives can be extracted from soil and undergo subsequent controlled decomposition. Subcritical water has been used as a solvent and reagent for the hydrolysis of triglycerides, some containing unsaturated acids, in the temperature range from 260°C to 280°C. Food flavourings can be obtained by extraction and subsequent reaction of the extract. Coffee flavourings can be obtained from green coffee beans when they are extracted in the presence of oxygen.

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Superheated water is extremely dangerous...people have been severely injured by such water

There have been reports of serious skin burns and scalding injuries around people’s hands and faces as a result of hot water erupting out of a cup after it had been over-heated in a microwave oven. Overheating of water in a cup can result in superheated water (past its boiling temperature) without appearing to boil. Superheating occurs if water is heated in a container that does not assist the formation of bubbles, which is a visual sign of boiling. Glass containers are the most likely to superheat water because their surfaces have few or no defects. The presence of slight defects, dirt, or other impurities usually help the water boil because bubbles will form on these imperfections. Adding materials such as instant coffee or sugar before heating greatly reduces the possibility of super heating.

Water does not always boil when it is heated above its normal boiling temperature of 100°C or 212°F.

Water can always evaporate into dry air, but it normally only does so at its surface. When water molecules leave the surface faster than they return, the quantity of liquid water gradually diminishes. That is ordinary evaporation. However, when water is heated to its boiling temperature, it can begin to evaporate not only from its surface, but also from within. If no bubbles are leaving the surface of the water as it is being heated to the boiling point, or above, steam bubbles may be forming inside the hot water. Water molecules then can evaporate into that steam bubble and make it grow larger and larger. When the water is disturbed in some way, it will boil violently. This may happen by inserting a fork or spoon into the water or striking the bottom of the container – and an explosion follows. When water is sufficiently superheated, all that is needed is just a single “seed” bubble to start an explosion and empty the container completely. This situation becomes even worse if the top surface of the water is “sealed” by a thin layer of oil or fat so that normal evaporation cannot occur.

Mild superheating happens fairly often and we rarely think much about it as we sponge up the spilled liquid inside the microwave oven. Severe superheating is less common but is a very dangerous phenomenon.

What Can Consumers Do to Avoid Super-Heated Water?

First: Follow the precautions and recommendations found in the microwave oven instruction manuals, specifically the heating time.

* Do not use excessive amounts of time when heating water or liquids in the microwave oven.
* Determine the best time setting to heat the water just to the desired temperature and use that time setting regularly.

If you really need to boil water, be very careful with it after microwaving or boil it on a stovetop instead. When you heat water on the stove, the hot spots at the bottom of the pot or defects in the pot bottom usually assist steam bubble formation so that boiling occurs soon after the boiling temperature is reached. Cooking water too long on a stovetop means that some of it boils away, but doing the same in a microwave oven may mean that it becomes dangerously superheated. Just a reminder that boiling water is a hazard for children even without superheating.

Second: Handle liquids that have been heated in a microwave oven with respect.

* Do not remove a liquid the instant the oven stops. If the water was bubbling
spasmodically or not at all despite heavy heating, it may be superheated and deserves particular respect. But even if you see no indications of superheating, it takes no real effort to be careful. If you cooked the water or any other liquid long enough for it to reach boiling temperature, let it rest for a minute per cup before removing it from the microwave.
* Never put your face or body over the container and keep the container at a safe
distance when you add things to it for the first time: powdered coffee, sugar, a
teabag, or a spoon. The spontaneous bubbling that occurs when you add something to microwave-heated water is the result of such mild superheating. It is far better to have the liquid boil violently while it is inside the microwave oven than when it is outside on your counter and can splatter all over you.

Finally: This is not meant to scare you away from using your microwave oven or from heating water in it. It is intended to show you that there is a potential hazard that you can avoid. Microwave ovens are wonderful devices as long as you use them properly.

“Using them properly” means not heating liquids too long in smooth-walled containers.

Answer 10

dunno much abt it
its temp is 420k