Boiling is the process of transition of a substance from a liquid to a gaseous state (vaporization in a liquid). Boiling is not evaporation: it differs in what can happen only at a certain pressure and temperature.
Boiling – heating water to boiling point.
Boiling of water is a complex process that occurs in four stages. Consider the example of boiling water in an open glass vessel.
At the first stage When water boils, small air bubbles appear at the bottom of the vessel, which can also be seen on the surface of the water on the sides.
These bubbles are formed as a result of the expansion of small air bubbles that are found in small cracks in the vessel.
At the second stage an increase in the volume of bubbles is observed: more and more air bubbles rush to the surface. There is saturated steam inside the bubbles.
As the temperature rises, the pressure of the saturated bubbles increases, causing them to increase in size. As a result, the Archimedean force acting on the bubbles increases.
It is thanks to this force that the bubbles tend to the surface of the water. If the top layer of water has not had time to warm up up to 100 degrees C(and this is the boiling point of pure water without impurities), then the bubbles sink down into hotter layers, after which they rush back to the surface again.
Due to the fact that the bubbles are constantly decreasing and increasing in size, sound waves arise inside the vessel, which create the noise characteristic of boiling.
At the third stage A huge number of bubbles rise to the surface of the water, which initially causes a slight cloudiness of the water, which then “turns pale.” This process does not last long and is called “white boiling”.
Finally, at the fourth stage After boiling, the water begins to boil intensely, large bursting bubbles and splashes appear (as a rule, splashes mean that the water has boiled strongly).
Water vapor begins to form from the water, and the water makes specific sounds.
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Steam temperature when water boils ^
Steam is the gaseous state of water. When steam enters the air, it, like other gases, exerts a certain pressure on it.
During the process of steam formation, the temperature of the steam and water will remain constant until all the water has evaporated.
This phenomenon is explained by the fact that all the energy (temperature) is directed towards turning water into steam. In this case, dry saturated steam is formed. There are no highly dispersed particles of the liquid phase in such vapor. Also steam can be.
saturated wet and overheated Saturated steam containing suspended highly dispersed particles of the liquid phase , which are evenly distributed throughout the entire mass of steam, is called.
wet saturated steam At the beginning of boiling water, just such steam is formed, which then turns into dry saturated steam. Steam, the temperature of which is higher than the temperature of boiling water, or rather superheated steam, can only be obtained using special equipment..
In this case, such steam will be close in its characteristics to gas
Boiling point of salt water^ The boiling point of salt water is higher than the boiling point of fresh water . Consequently salt water boils later than fresh water
. Salt water contains Na+ and Cl- ions, which occupy a certain area between the water molecules.
In salt water, water molecules attach to salt ions in a process called hydration. The bond between water molecules is much weaker than the bond formed during hydration.
Therefore, when fresh water molecules boil, vaporization occurs faster.
Boiling water with dissolved salt will require more energy, which in this case is temperature.
As the temperature increases, the molecules in salt water move faster, but there are fewer of them, causing them to collide less often. As a result, less steam is produced, the pressure of which is lower than that of fresh water steam. In order for the pressure in salt water to become higher than atmospheric pressure and the boiling process to begin, a higher temperature is required.
Oleg
Nastya
What causes water to boil at high temperatures?
Superheated steam is steam with a temperature above 100C (well, if you are not in the mountains or a vacuum, but under normal conditions), it is obtained by passing steam through hot tubes, or, more simply, from a boiling solution of salt or alkali (dangerous - alkali is stronger than Na2CO3 (for example potash - K2CO3 why NaOH residues become harmless to the eyes within a day or two, unlike KOH residues carbonated in air) saponifies the eyes, don’t forget to wear swimming goggles!), but such solutions boil in bursts, you need boiling pots and a thin layer on bottom, water can be added when boiling, only it boils away.
So from boiling salt water you can get steam with a temperature of about 110C, no worse than the same from a hot 110C pipe, this steam contains only water and is heated, he doesn’t remember how, but it has a “power reserve” of 10C compared to steam from a fresh water kettle.
It can be called dry, because... warming (by contacting as in a pipe, or even by radiation, characteristic not only of the sun but also of any body to some (temperature-dependent) degree) an object, steam can, having cooled to 100C, still remain a gas, and only further cooling below 100C will cause its condensation into a drop of water, and almost a vacuum (saturated steam pressure of water is about 20 mm Hg from 760 mm Hg (1 atm), that is, 38 times lower than atmospheric pressure, this also happens with unsuperheated, saturated steam with a temperature of 100 C in a heated vessel (kettle from a spout which steams out), and not only with water, but with any boiling substance, for example, medicinal ether boils already at body temperature, and can boil in a flask in the palm, from the neck of which its vapors will “fountain”, noticeably refracting light, if now close the flask with the second palm, and remove the heating of the lower palm, replacing it with a stand with a temperature below 35C, the ether will stop boiling, and its saturated steam, which pushed out all the air from the flask during boiling, will condense into a drop of ether, creating a vacuum no stronger than the one from which the ether boils, that is, approximately equal to the pressure of saturated vapor of the ether at the temperature of the coldest point inside the flask, or a second vessel or hose attached to it without leaks with the far end closed, this is how the Kriofor device is designed, demonstrating the principle of a cold wall, like sweet Velcro - bees, capturing all the vapor molecules in the system. (“Vacuum alcohol” is driven this way, without heating)
And at more than 1700 Celsius, water very well decomposes into oxygen and hydrogen... it turns out to be a bad boom, there’s no need to splash it on all sorts of burning metal-Sicambrican structures
Why is it easier to swim in salt water than in fresh water?
It is easier to swim in salt water than in fresh water because salt makes the water heavier: if you take two tanks of the same capacity, one containing salt water and the other containing fresh water, the tank with salt water will weigh a little more. And the greater the density (weight) of water, the easier it is to swim in it.
An object can float in a liquid if its weight is equal to the weight of the water it displaces or pushes out (the water is displaced to make room for the object). You can look at it from the other side: when you sit in the bathtub, you see that the water level in it is rising. If you knock down the water that your body has displaced, the weight of that water will be equal to the weight of your body. If the water has a higher density, like salt water, then your body will displace less of it (i.e., less water will be needed to equal your body weight), and you will emerge higher than if you had surfaced in fresh water.
The first glass contains regular fresh water, the second glass contains salt water,
in the third - very salty.
Which retains heat better: fresh or salt water?
Two vessels were filled with fresh water. They were heated for about 10 minutes. Then, 2 tablespoons of salt were added to one of the containers and labeled “salt water.” On the first try, there was no noticeable difference; the temperature was 120 degrees. On the second try, we added 2 more tablespoons of salt and the difference became noticeable. Salt water cooled much faster than regular tap water. As part of the experiment, the amount of salt in the water was monitored. When the water temperature reached 90 degrees, data collection began. The same thermometers were used throughout the experiment.
Why is the water in the ocean salty?
Salt from the Earth's surface constantly dissolves and ends up in the ocean.
If all the oceans were dried up, the remaining salt could be used to build a wall 230 km high and almost 2 km thick. Such a wall could circle the entire globe along the equator. Or another comparison. The salt of all the dried up oceans is 15 times larger in volume than the entire European continent!
Regular salt is obtained from sea water, salt springs, or from the development of rock salt deposits. Sea water contains 3-3.5% salt. Inland seas, such as the Mediterranean Sea, Red Sea, contain more salt than open seas. The Dead Sea, occupying only 728 square meters. km., contains approximately 10,523,000,000 tons of salt.
On average, a liter of sea water contains about 30 g of salt. Rock salt deposits in various parts of the earth were formed many millions of years ago as a result of the evaporation of sea water. To form rock salt, nine-tenths of the volume of sea water must evaporate; It is believed that inland seas were located on the site of modern deposits of this salt. They evaporated faster than new sea water came in - so rock salt deposits appeared.
The main amount of table salt is obtained from rock salt. Usually, mines are laid to salt deposits. Clean water is pumped through the pipes, which dissolves the salt. Through the second pipe this solution rises to the surface.
Why does fresh water boil faster than salt water?
Salt water boils at a higher temperature than fresh water; therefore, under the same heating conditions, fresh water will boil faster, salt water will boil later. There is a whole physico-chemical theory why this is the case, but “on the fingers” it can be explained as follows. Water molecules bind to salt ions - the process of hydration occurs. The bond between water molecules is weaker than the bond formed by hydration. Therefore, a fresh water molecule is more easily (at a lower temperature) separated from its “surroundings” - i.e. roughly speaking, it evaporates. And in order for a water molecule with dissolved salt to “escape from the embrace” of salt and other water molecules, more energy is required, i.e. high temperature.
Boiling is the process of changing the state of aggregation of a substance. When we talk about water, we mean the change from a liquid state to a vapor state. It is important to note that boiling is not evaporation, which can occur even at room temperature. It should also not be confused with boiling, which is the process of heating water to a certain temperature. Now that we have understood the concepts, we can determine at what temperature water boils.
Process
The process of transforming the state of aggregation from liquid to gaseous is complex. And although people don't see it, there are 4 stages:
- At the first stage, small bubbles form at the bottom of the heated container. They can also be seen on the sides or on the surface of the water. They are formed due to the expansion of air bubbles, which are always present in the cracks of the container where the water is heated.
- In the second stage, the volume of bubbles increases. They all begin to rush to the surface, since inside them there is saturated steam, which is lighter than water. As the heating temperature increases, the pressure of the bubbles increases, and they are pushed to the surface thanks to the well-known Archimedes force. In this case, you can hear the characteristic sound of boiling, which is formed due to the constant expansion and reduction in the size of the bubbles.
- At the third stage, a large number of bubbles can be seen on the surface. This initially creates cloudiness in the water. This process is popularly called “white boiling,” and it lasts a short period of time.
- At the fourth stage, the water boils intensely, large bursting bubbles appear on the surface, and splashes may appear. Most often, splashing means that the liquid has reached its maximum temperature. Steam will begin to emanate from the water.
It is known that water boils at a temperature of 100 degrees, which is possible only at the fourth stage.
Steam temperature
Steam is one of the states of water. When it enters the air, it, like other gases, exerts a certain pressure on it. During vaporization, the temperature of steam and water remains constant until the entire liquid changes its state of aggregation. This phenomenon can be explained by the fact that during boiling, all the energy is spent on converting water into steam.
At the very beginning of boiling, moist, saturated steam is formed, which becomes dry after all the liquid has evaporated. If its temperature begins to exceed the temperature of water, then such steam is overheated, and its characteristics will be closer to gas.
Boiling salt water
It is quite interesting to know at what temperature water with a high salt content boils. It is known that it should be higher due to the content of Na+ and Cl- ions in the composition, which occupy the area between water molecules. This makes the chemical composition of water with salt different from ordinary fresh liquid.
The fact is that in salt water a hydration reaction takes place - the process of adding water molecules to salt ions. The bonds between fresh water molecules are weaker than those formed during hydration, so it will take longer for a liquid with dissolved salt to boil. As the temperature rises, the molecules in salty water move faster, but there are fewer of them, causing collisions between them to occur less often. As a result, less steam is produced, and its pressure is therefore lower than the steam pressure of fresh water. Consequently, more energy (temperature) will be required for complete vaporization. On average, to boil one liter of water containing 60 grams of salt, it is necessary to increase the boiling degree of water by 10% (that is, by 10 C).
Dependence of boiling on pressure
It is known that in the mountains, regardless of the chemical composition of the water, the boiling point will be lower. This occurs because the atmospheric pressure is lower at altitude. Normal pressure is considered to be 101.325 kPa. With it, the boiling point of water is 100 degrees Celsius. But if you climb a mountain, where the pressure is on average 40 kPa, then the water there will boil at 75.88 C. But this does not mean that you will have to spend almost half as much time cooking in the mountains. Heat treatment of foods requires a certain temperature.
It is believed that at an altitude of 500 meters above sea level, water will boil at 98.3 C, and at an altitude of 3000 meters, the boiling point will be 90 C.
Note that this law also applies in the opposite direction. If you place a liquid in a closed flask through which steam cannot pass, then as the temperature rises and steam forms, the pressure in this flask will increase, and boiling at increased pressure will occur at a higher temperature. For example, at a pressure of 490.3 kPa, the boiling point of water will be 151 C.
Boiling distilled water
Distilled water is purified water without any impurities. It is often used for medical or technical purposes. Considering that there are no impurities in such water, it is not used for cooking. It is interesting to note that distilled water boils faster than ordinary fresh water, but the boiling point remains the same - 100 degrees. However, the difference in boiling time will be minimal - only a fraction of a second.
In a teapot
People often wonder at what temperature water boils in a kettle, since these are the devices they use to boil liquids. Taking into account the fact that the atmospheric pressure in the apartment is equal to standard, and the water used does not contain salts and other impurities that should not be there, then the boiling point will also be standard - 100 degrees. But if the water contains salt, then the boiling point, as we already know, will be higher.
Conclusion
Now you know at what temperature water boils, and how atmospheric pressure and the composition of the liquid affect this process. There is nothing complicated about this, and children receive such information at school. The main thing is to remember that as the pressure decreases, the boiling point of the liquid also decreases, and as it increases, it also increases.
On the Internet you can find many different tables that indicate the dependence of the boiling point of a liquid on atmospheric pressure. They are available to everyone and are actively used by schoolchildren, students and even teachers at institutes.
Boiling is the process of vaporization that occurs when a liquid is brought to the boiling point. Every person knows from his school desk that water boils at t=100˚С. But many are interested in the question of which water boils faster: salted or fresh?
What is the boiling process?
Boiling is a rather complex process consisting of four stages:
- First stage characterized by the appearance of small air bubbles that appear both on the surface of the liquid and on the side. Their occurrence is the result of the expansion of air bubbles located in microscopic cracks in the container.
- During the second stage you can see that the bubbles increase in volume and more and more of them appear on top. This phenomenon is explained by an increase in temperature, at which the pressure on the bubbles increases. Thanks to Archimedean force, they appear on the surface. If it does not have time to warm up to the boiling temperature (100˚C), then the bubbles again go to the bottom, where the water is hotter. The noise characteristic of boiling is created as the size of the bubbles increases and decreases.
- At the third stage a mass of bubbles is observed, which, rising to the surface, causes short-term turbidity of the water.
- Fourth stage characterized by intense seething and the appearance of large bubbles, which, when bursting, create splashes. The latter indicate that the water has boiled. Water vapor appears, and the water makes sounds characteristic of boiling.
Fresh water boiling
Boiling water is water brought to a boil. During this process, abundant steam formation occurs, which is accompanied by the release of free oxygen molecules from the boiling liquid. Due to prolonged exposure to high temperatures, microbes and pathogenic bacteria die in boiling water. Therefore, if the quality of tap water is poor, it is undesirable to consume it raw.
Fresh but hard water contains salts. During boiling, they form a coating on the walls of the kettle, which is more often called scale. Boiling water is commonly used to prepare hot drinks or disinfect fruits or vegetables.
When salt water boils
Experiments show that the boiling point of salt water is higher than the boiling point of fresh water. Therefore, we can conclude that fresh water boils faster. Salt water contains chlorine and sodium ions, which are found among the water molecules. Between them, the process of hydration occurs - the addition of water molecules to salt ions.
It is worth noting that the hydration bond is much stronger than the water intermolecular bond. Therefore, when fresh water boils, the process of vaporization begins faster. A liquid with salts dissolved in it requires a little more energy to boil, which in this situation is temperature.
When it increases, molecules in salt water move much faster, but their number decreases, which means they collide less often. This is what can explain the smaller amount of steam - after all, its pressure is less than that of fresh water. To achieve greater than atmospheric pressure in salt water and begin to boil, a higher temperature is required.
Another justification
When cooking, many housewives salt the water at the beginning of the process, citing the fact that it will boil faster this way. And some find an explanation for why salt water boils faster, relying on school knowledge of a physics course, namely the topic related to heat transfer. As is known, heat transfer is of three types: heat transfer, which is characteristic of solids, convection, which is present in gaseous and liquid bodies, and radiation.
The latter type of heat transfer exists even in space. This is confirmed by the stars and, of course, the sun. But still, the main factor in this matter is density. Since salt water has a higher density than fresh water, it boils faster. At the same time, it takes more time to freeze. Consequently, with a denser liquid, heat transfer will be more active and boiling will occur faster.
Boiling water at reduced pressure: Video
I wrote in Russian that boiling water LIE
No, this is not Russian.
Quote: Vladimir S
Just don’t eat all the boiling water in surprise.
Very simple and memorable advice on how to forever stop confusing these verbs with similar semantic loads.
So, the verb “to lie” without a prefix is not used. Therefore, if you desperately need to use it, then feel free to add any prefix that makes sense and go ahead: put, lay out, lay out, rearrange, fold, etc.
But the verb “put,” on the contrary, for some reason does not like prefixes. But he loves it when the emphasis is placed correctly: klaU, klaDI, klaLA (incorrectly - klaLA), the participle klAvshiy, the gerund kladYA.
Only a chemist can benefit from Google Chemistry
It depends on the individual. You can look at a book and see nothing.
The scale in the kettle is salt, albeit sparingly soluble, i.e. theoretically, water in a kettle with scale will boil at t greater than 100
And it turned out that the sea is salty, because salty herrings swim in it
Theoretically, in terms of b.b. and b.m. magnitudes, salted herrings thrown into a fresh sea can make it salty. Again, we need to see how many herrings there will be.
Without increasing the pressure above one hundred degrees, even Einstein will not heat it up.
He can’t do this in a laboratory, but an ordinary citizen, in an ordinary kitchen, in an ordinary microwave, can do it easily.
And further
And in general, the North was not interested in some kind of boiling centers, but why the bonds in hydrated ions
This is definitely not what interests him.
Quote: North
if you salt water, it will boil faster
As we have seen many times above, water without salt can easily be overheated, but it will take longer. If you salt it in advance, it will take less time, the water will not be overheated, it will boil at 100°C.
And despite the fact that with increasing salt concentration, water begins to boil at a higher temperature, but theoretically it turns out that if you add salt, it will boil earlier. But the examples show that not only theoretically, but also quite practically. And why did he say theoretically - because it is still desirable, if not necessary, to take purified or even distilled water, and the dishes should be clean and smooth.
You don't always see this in a regular kitchen. Usually we boil whatever water we have, often even from the tap, in an ordinary scratched container, and add salt not for tea, but for soup, that is, along with the salt, there are other ingredients there. There can be no talk of any overheating here. But the person who asked the question did not provide details.
Boilers are neutral and do not affect the boiling point.
the boiling pots are placed in the water even before heating begins
Boilers are a developed, rough, spongy, porous surface. We will consider in this capacity the surface roughness of the glass bulb.
1. Flask with fresh bidistillate. Everything is clean everywhere.
2. A flask with a roughness invisible to the eye.
3. A flask with a bottom scratched from the inside with sandpaper.
In all three, the boiling point will be different. Boiling, that's exactly what I was talking about North. Although the temperature boiling in all three cases, of course, it will be the same.
By the way, food should be salted after it is ready. I almost I don't add salt. Not after reading Bragg, but since childhood, such are taste preferences.