The temperature of boiling water in a kettle. At what temperature does water boil in an electric kettle?

Boiling water is accompanied by changes in the features of its phase state and the acquisition of a vaporous consistency when certain temperature indicators are reached.

In order to boil water and contribute to the release of steam, a temperature of 100 degrees Celsius is required. Today we will try to deal with the question of how to understand that the water has boiled.

Ever since childhood, we have all heard parental advice regarding the fact that you can only use boiled water. Today, one can meet both supporters and opponents of such recommendations.

On the one hand, boiling water is actually necessary and useful procedure, because it is accompanied by the following positive aspects:

• Reaching water temperatures of 100 degrees and above is accompanied by the death of many pathogens, so boiling can be called a kind of purification of the liquid. For effective fight With bacteria, experts recommend boiling water for at least 10 minutes.
• When boiling water, various impurities are also eliminated, which can pose a certain danger to human health. A sign of getting rid of impurities is the formation of scale, which we often see on the walls of kettles and pots. But keep in mind that brewing tea only with boiled water, there is a high probability of regular filling of the body with crystallized deposits, which is fraught with the development of urolithiasis in the future.

The harm of boiling water may be due to non-compliance with the indicated recommendations regarding the time of boiling.

If you brought the liquid to 100 degrees and at the same time immediately removed it from the heat, there is no doubt that the predominant number of microorganisms were not exposed to negative impact. To avoid this, be sure to boil water for 10 to 15 minutes.

One more negative side boiling water enters the loss of oxygen, which is a vital element for any living organism.

Thanks to large oxygen molecules, the distribution of useful elements is ensured through circulatory system. Of course, the lack of oxygen is not detrimental to health, but it does not represent any benefit.

There are several methods for bringing water to a boil. They differ, first of all, in what pud you use to boil the liquid. Kettles are most often used to make tea or coffee, but pots are most often used in cooking.

So, first you need to fill the kettle with cold tap water and place the container on the fire. As it warms up, crackling sounds will be clearly audible, which will be replaced by an increasing hiss.

The next stage is the fading of the hiss, which is replaced by a faint noise, the appearance of which is accompanied by the release of steam. These signs will indicate that the water in the kettle has boiled. It remains only to wait about 10 minutes and remove the kettle from the heat.

It is much easier to determine the boiling of water in open containers. Fill the pot necessary quantity cold water and place the container on the fire. The first signs that the water will soon boil will be the appearance of small bubbles that form at the bottom of the container and rise to the top.

The next step is an increase in the size and number of bubbles, which is accompanied by the formation of steam above the surface of the container. If the water begins to boil, then the liquid has reached the temperature required for boiling.

The following facts will be quite useful for you:

• If you want to bring water to a boil as quickly as possible using a saucepan, be sure to cover the container with a lid to retain heat. You also need to remember that in large containers, water reaches a boil longer, which is associated with the expenditure of more time to heat such a pan.
• Use only cold tap water. The fact is that hot water may contain impurities of lead in the plumbing system. According to many experts, such water is not suitable for consumption and use in cooking, even after boiling.
• Never fill containers to the brim, as water will overflow from the pot as it boils.
• As the altitude increases, the boiling point decreases. In such a case, more boiling time may be required to ensure that all pathogens are killed. This fact should be taken into account when going hiking in the mountains.

Also, all precautions should be taken when contacting not only with hot water, a container, but also with the generated steam, which can cause serious burns.

If a liquid is heated, it will boil at a certain temperature. When boiling, bubbles form in the liquid, which rise to the top and burst. The bubbles contain air containing water vapor. When the bubbles burst, the vapor escapes, and thus the liquid evaporates rapidly.

Various substances that are in the liquid state boil at their own characteristic temperature. Moreover, this temperature depends not only on the nature of the substance, but also on atmospheric pressure. So water at normal atmospheric pressure boils at 100 ° C, and in the mountains, where the pressure is lower, water boils at a lower temperature.

When a liquid boils, the further supply of energy (heat) to it does not increase its temperature, but simply maintains boiling. That is, energy is spent on maintaining the boiling process, and not on raising the temperature of the substance. Therefore, in physics, such a concept is introduced as specific heat of vaporization(L). It is equal to the amount of heat required to completely boil away 1 kg of liquid.

It is clear that different substances have their own specific heat of vaporization. So for water it is equal to 2.3 10 6 J/kg. For ether, which boils at 35 °C, L = 0.4 10 6 J/kg. Mercury boiling at 357 °C has L = 0.3 10 6 J/kg.

What is the boiling process? When the water heats up, but has not yet reached its boiling point, small bubbles begin to form in it. They usually form at the bottom of the tank, as they usually heat up under the bottom, and there the temperature is higher.

Bubbles are lighter than the surrounding water and therefore begin to rise to the upper layers. However, here the temperature is even lower than at the bottom. Therefore, the vapor condenses, the bubbles become smaller and heavier, and again fall down. This happens until all the water is heated to the boiling point. At this time, a noise is heard that precedes boiling.

When the boiling point is reached, the bubbles no longer sink down, but float to the surface and burst. Steam comes out of them. At this time, it is no longer noise that is heard, but the gurgling of the liquid, which indicates that it has boiled.

Thus, during boiling, as well as during evaporation, there is a transition of liquid into vapor. However, unlike evaporation, which occurs only on the surface of a liquid, boiling is accompanied by the formation of bubbles containing vapor throughout the volume. Also, unlike evaporation, which occurs at any temperature, boiling is possible only at a certain temperature characteristic of a given liquid.

Why is the higher the atmospheric pressure, the higher the boiling point of a liquid? The air presses on the water, and therefore pressure is created inside the water. When bubbles form, the vapor also presses into them, and more strongly than external pressure. The greater the pressure from the outside on the bubbles, the stronger the internal pressure must be in them. Therefore, they form at a higher temperature. This means that water boils at a higher temperature.

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 certain pressures and temperatures.

Boiling - heating water to boiling point.

The boiling of water is a complex process that takes place in four stages. Consider the example of boiling water in an open glass vessel.

At the first stage boiling water at the bottom of the vessel, small air bubbles appear, which can also be seen on the surface of the water on the sides.

These bubbles form 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 break to the surface. Inside the bubbles is saturated steam.

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 did not have time to warm up up to 100 degrees C(and this is the boiling point pure water without impurities), then the bubbles sink down into the hotter layers, after which they again rush back to the surface.

Due to the fact that the bubbles are constantly decreasing and increasing in size, sound waves are generated 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 turbidity of the water, which then “turns pale”. This process does not last long and is called "boiling with a white key."

Finally, at the fourth stage boiling 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, while the water makes specific sounds.

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Steam temperature at boiling water^

Steam is the gaseous state of water. When steam enters the air, it, like other gases, exerts a certain pressure on it.

In the process of vaporization, 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 to the conversion of water into steam.

AT this case dry saturated steam is produced. There are no highly dispersed particles of the liquid phase in such a pair. Also steam can be saturated wet and overheated.

Saturated steam containing suspended fine particles of the liquid phase, which are uniformly distributed over the entire mass of the vapor, is called wet saturated steam.

At the beginning of boiling water, just such steam is formed, which then turns into dry saturated. 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 fresh water . Consequently salty water boils later fresh. Salt water contains Na+ and Cl- ions, which occupy a certain area between water molecules.

In salt water, water molecules attach to salt ions, a process called hydration. The bond between water molecules is much weaker than the bond formed during hydration.

Therefore, when boiling from fresh water molecules, vaporization occurs faster.

Boiling water with dissolved salt will require more energy, which in this case is temperature.

As the temperature rises, the molecules in salt water begin to move faster, but there are fewer of them, so they 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 needed. When adding 60 grams of salt to 1 liter of water, the boiling point will increase by 10 C.

If you are asked at what temperature water boils, you will most likely answer that at 100 ° C. And your answer will be correct, but this value is only true at normal atmospheric pressure - 760 mm Hg. Art. In fact, water can boil at both 80°C and 130°C. In order to explain the reason for such discrepancies, it is first necessary to clarify what boiling is.

To figure out how many degrees are needed for the water to boil, studying the mechanism of this will help. physical phenomenon. Boiling is the process of converting liquid into vapor and takes place in several stages:

1. When the liquid is heated, bubbles with air and water vapor come out of the microcracks in the walls of the vessel.
2. The bubbles expand a little, but the liquid in the vessel is so cold that the vapor in the bubbles condenses.
3. The bubbles begin to burst until the entire thickness of the liquid becomes hot enough.
4. After some time, the pressure of water and steam in the bubbles equalize. At this stage, individual bubbles can rise to the surface and release steam.
5. The bubbles begin to rise intensively, seething begins with a characteristic sound. Starting from this stage, the temperature in the vessel does not change.
6. The boiling process will continue until all the liquid passes into a gaseous state.

Steam temperature

The temperature of the steam when water boils is the same as that of the water itself. This value will not change until all the liquid in the vessel has evaporated. During the boiling process, wet steam is formed. It is saturated with liquid particles uniformly distributed throughout the entire gas volume. Further, highly dispersed particles of the liquid condense, and the saturated steam turns into dry.

There is also superheated steam, which is much hotter than boiling water. But it can only be obtained with the help of special equipment.

Pressure influence

We have already found out that for a liquid to boil, it is necessary to equalize the pressure of a liquid substance and vapor. Since water pressure is the sum of atmospheric pressure and the pressure of the liquid itself, there are two ways to change the boiling time:

• change in atmospheric pressure;
• change in pressure in the vessel itself.

We can observe the first case in territories located at different heights above sea level. On the coasts, the boiling point will be 100 ° C, and at the top of Everest - only 68 ° C. The researchers calculated that when climbing mountains, the boiling point of water drops by 1 °C every 300 meters.

These values ​​may vary depending on chemical composition water and the presence of impurities (salts, metal ions, soluble gases).

Kettles are most often used to get boiling water. The boiling point of water in a kettle also depends on where you live. Mountain dwellers are advised to use autoclaves and pressure cookers, which help to make boiling water hotter and speed up the cooking process.

Boiling salt water

The temperature at which water boils determines the presence of impurities in it. As part of sea ​​water sodium and chloride ions are present. They are located between the H2O molecules and attract them. This process is known as hydration.

The bond between water and salt ions is much stronger than between water molecules. It takes more energy to boil salt water so that these bonds can be broken. This energy is temperature.

Also, salty liquid differs from fresh water by a low concentration of H2O molecules. In this case, when heated, they begin to move faster, but they cannot form a sufficiently large vapor bubble, since they collide less often. The pressure of small bubbles is not enough to bring them to the surface.

To equalize water and atmospheric pressure, you need to increase the temperature. Therefore, salt water takes much longer to boil than fresh water, and the boiling point will depend on the salt concentration. It is known that adding 60 g of NaCl to 1 liter of liquid increases the boiling point by 10 °C.

How to change the boiling point

In the mountains it is very difficult to cook food, it takes too much time. The reason is not enough hot boiling water. At very high altitudes, it is almost impossible to boil an egg, let alone cook meat that needs a good heat treatment.

Changing the temperature at which the liquid boils is important for residents not only of mountainous areas.

For sterilization of products and equipment, it is desirable to use more high temperature than 100 °C, as some microorganisms are heat resistant.

This is important information not only for housewives, but also for professionals working in laboratories. Also, increasing the boiling point can significantly save time spent on cooking, which is important in our time.

To increase this figure, you need to use a tightly closed container. Pressure cookers are best suited for this, in which the lid does not allow steam to pass through, increasing the pressure inside the vessel. During heating, steam is released, but since it cannot escape, it condenses on the inside of the lid. This leads to a significant increase in internal pressure. In autoclaves, the pressure is 1–2 atmospheres, so the liquid in them boils at a temperature of 120–130 °C.

The maximum boiling point of water is still unknown, since this figure can increase as long as atmospheric pressure increases. It is known that water cannot boil in steam turbines even at 400 °C and a pressure of several tens of atmospheres. The same data were obtained at great depths of the ocean.

Boiling Water Under Reduced Pressure: Video

Everyone who studied physics at school, when asked at what temperature water boils, will answer without hesitation: “100 ° C”, even if his grades were below average. But why, then, do climbers complain that at altitude they have a problem with cooking and brewing tea? Let's talk about this in more detail.

Boiling - physical process converting liquid to steam. The boiling point of a liquid directly depends on its composition and atmospheric pressure. Therefore, the higher we climb the mountains, the less pressure becomes, and the water needs a lower temperature to boil.

At 0 altitude above sea level, the boiling point of water is actually 100 °C. But with each ascent of 500 meters, the boiling point of water decreases by 2–3 °C. At an altitude of 1000 m, water will boil at a temperature of 96.7 ° C. At 2000 m, it needs only 93.3 ° C to boil.

On Elbrus, the highest peak in Europe (5642 m), where at the end of summer the temperature reaches -7°C, water will boil at 80.8°C.

At the top of the Caucasian Kazbek (5033 m), it takes 83 °C to boil water.

In the Himalayas, where the height of the mountains reaches almost 9 thousand meters above sea level, the water will need an even lower temperature to boil. On the very high mountain Himalayas - Annapurna - water will boil at about 70.7 ° C.

In the mountains of Kazakhstan, the boiling point of water is different:

• On the highest mountain of Kazakhstan, Khan-Tengri (7010 m) - 75.5 ° C.
• At Talgar peak (4979) - 83.3 °С.
• At Aktau (4690) - 84.3 °C.
• On Belukha (4506) - 84.9 ° С.

As the pressure increases, the boiling point of water also increases. Therefore, in a special dish that provides high pressure when cooking, for example in a pressure cooker, food cooks much faster.

It is no coincidence that mountain dwellers are among the top buyers of household pressure cookers. And for lovers of mountain hiking, they produce special dishes that provide a high boiling point of water.

As you know, when boiling water goes through several stages:

• the formation of air bubbles when the temperature rises;
• increase in bubbles and their rise to the surface;
• clouding of the surface due to bubbles accumulated on it;
• bubbling of water due to the rupture of bubbles and the formation of steam.

It should be noted that the boiling point of salt water is higher than that of fresh water, since salt ions between water molecules give them greater strength. As a result, in order to break the bond and form steam, a higher temperature is needed. For example, 40 g of salt will increase the boiling point of a liter of water by almost 1 °C.

When answering the question at what temperature water boils, do not forget that a lot depends on atmospheric pressure and the composition of water.