At what temperature does water boil in an electric kettle. How to boil water correctly and what temperature is needed to brew tea How does it boil

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 made up of atmospheric pressure and the pressure of the liquid itself, you can change the boiling time in two ways:

• 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 a temperature higher 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 was obtained from great depths ocean.

Boiling Water Under Reduced Pressure: Video

Boiling- This is an intense transition of liquid to vapor, occurring with the formation of vapor bubbles throughout the entire volume of the liquid at a certain temperature.

During boiling, the temperature of the liquid and vapor above it does not change. It remains unchanged until all the liquid boils away. This is because all the energy supplied to the liquid is spent on turning it into vapor.

The temperature at which a liquid boils is called boiling point.

The boiling point depends on the pressure exerted on the free surface of the liquid. This is due to the dependence of saturated vapor pressure on temperature. A vapor bubble grows as long as the pressure of the saturated vapor inside it slightly exceeds the pressure in the liquid, which is the sum of the external pressure and the hydrostatic pressure of the liquid column.

The greater the external pressure, the more boiling temperature.

Everyone knows that water boils at 100 ºC. But we should not forget that this is true only at normal atmospheric pressure (about 101 kPa). With an increase in pressure, the boiling point of water increases. So, for example, in pressure cookers, food is cooked under a pressure of about 200 kPa. The boiling point of water reaches 120°C. In water of this temperature, the cooking process is much faster than in ordinary boiling water. This explains the name "pressure cooker".

Conversely, by reducing the external pressure, we thereby lower the boiling point. For example, in mountainous areas(at an altitude of 3 km, where the pressure is 70 kPa) water boils at a temperature of 90 °C. Therefore, the inhabitants of these areas, using such boiling water, require much more time for cooking than the inhabitants of the plains. And to cook in this boiling water, for example, a chicken egg is generally impossible, since at a temperature below 100 ° C the protein does not coagulate.

Each liquid has its own boiling point, which depends on the saturation vapor pressure. The higher the saturated vapor pressure, the lower the boiling point of the corresponding liquid, since at lower temperatures the saturated vapor pressure becomes equal to atmospheric pressure. For example, at a boiling point of 100 ° C, the pressure of saturated water vapor is 101,325 Pa (760 mm Hg), and vapor pressure is only 117 Pa (0.88 mm Hg). Mercury boils at 357°C at normal pressure.

The heat of vaporization.

Heat of vaporization (heat of vaporization)- the amount of heat that must be reported to the substance (at constant pressure and constant temperature) for the complete transformation of a liquid substance into vapor.

The amount of heat required for vaporization (or released during condensation). To calculate the amount of heat Q, necessary for the transformation into vapor of a liquid of any mass, taken at the boiling point, you need specific heat vaporization r mind-knife to the mass m:

When steam condenses, the same amount of heat is released.

Anton

Gennady  The boiling point of water is 100 degrees.

from 85 to 110 depending on pressure. Alyona.

Artem  depends on pressure. if high above sea level, then water boils at temperatures less than 100 degrees

Boris  100 degrees Celsius at the time of shutdown. If it's boiling water. The temperature is higher - it's already steam.

Sasha  98 degrees

Svetlana  temperature... 99.9 ... karoch about 100 degrees)))

Egor  There is the temperature at which the thermostat is set. Plus or minus error.

Peter  temperature exceeds 100Fyodor

Oksana  100 degrees... and went downhill...

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Tea brewing temperature

How to simply ensure the temperature of tea brewing if the kettle has no temperature controller and no thermometer?
Boil water, and cool, diluted with water at room temperature in a certain proportion.
For example, you need water for brewing at a temperature of 80 degrees.
1. Pour a liter of water into the kettle, bring to a boil.
2. We are waiting for the boiling to stop.
3. After the boiling stops, pour one and a half glasses of water at room temperature into the kettle.
4. Immediately pour into the teapot, and it will be 80 degrees.
What is happening there?
Step by step.
Under normal conditions (I do not consider mountainous conditions), water boils at 100 degrees.
1. Pour a liter of water into the kettle, bring to a boil. This will get the temperature very close to 100 degrees. Boiling takes place at a constant temperature.
2. We are waiting for the boiling to stop. By diluting, we want to lower the temperature of the water in the kettle, and not waste its energy consumption also on stopping boiling.
3. After the boiling stops, pour one and a half glasses of water at room temperature into the kettle. Why one and a half?
How much water to add? Unknown volume = X.
It was: 1000 ml * 100 degrees + X ml * 25 degrees.
Now: 1000 ml * 80 degrees + X ml * 80 degrees.
1000 * 100 + X * 25 = 1000 * 80 + X * 80,
1000 * 100 - 1000 * 80 = X * 80 - X * 25,
X \u003d 20000 / 55 \u003d 364 ml.
It's about a glass and a half.
Given the heat capacity of the teapot and teapot (heavy and unheated teapot), you can pour less.

At what temperature does water boil? | Q&A | Around...

31 Mar 2007 ... It would seem that the answer to this question is obvious - water boils at 100°C and freezes at 0°C (strictly adhering to physical...

Boiling is the process of changing the aggregate state of a substance. When we talk about water, we mean change. liquid state into vapor. It is important to note that boiling is not evaporation, which can occur even at room temperature. Also, do not confuse 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 very process of transforming the state of aggregation from liquid to gaseous is complex. And although people do not see it, there are 4 stages:

1. In 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 tank, where the water is heated.
2. In the second stage, the volume of the bubbles increases. All of them begin to rush to the surface, as there is saturated steam inside them, which is lighter than water. With an increase in the heating temperature, the pressure of the bubbles increases, and they are pushed to the surface due 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.
3. At the third stage, on the surface one can see a large number of bubbles. This initially creates cloudiness in the water. This process is popularly called "boiling with a white key", and it lasts a short period of time.
4. At the fourth stage, the water boils intensively, large bursting bubbles appear on the surface, and splashes may appear. Most often, splashing means that the liquid has heated up to maximum temperature. Steam will start to come out of 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, then, like other gases, it exerts a certain pressure on it. During vaporization, the temperature of the steam and water remain constant until all the liquid changes its temperature. 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, after the evaporation of all the liquid, becomes dry. If its temperature begins to exceed the temperature of water, then such steam is superheated, and in terms of its characteristics it will be closer to gas.

Boiling salt water

It is interesting enough 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 an area between water molecules. This chemical composition of water with salt differs from the usual fresh liquid.

The fact is that in salt water a hydration reaction takes place - the process of attaching water molecules to salt ions. Communication between molecules fresh water weaker than those formed during hydration, so boiling of a liquid with dissolved salt will take longer. As the temperature rises, the molecules in water containing salt move faster, but there are fewer of them, which is why collisions between them occur less frequently. As a result, less steam is produced and its pressure is therefore lower than the steam head of fresh water. Therefore, more energy (temperature) is required for full vaporization. On average, to boil one liter of water containing 60 grams of salt, it is necessary to raise the boiling point of water by 10% (that is, by 10 C).

Boiling pressure dependences

It is known that in the mountains, regardless of the chemical composition of water, the boiling point will be lower. This is 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 will boil there at 75.88 C. But this does not mean that cooking in the mountains will take almost half the time. For heat treatment products need 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 to reverse direction. If a liquid is placed in a closed flask through which vapor cannot pass, then with an increase in temperature and the formation of steam, the pressure in this flask will increase, and boiling at high blood pressure will happen at more high 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. Given 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

Often people are interested in what temperature water boils in a kettle, since it is these devices that they use to boil liquids. Taking into account the fact that the atmospheric pressure in the apartment is equal to the standard one, 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 in this, and children receive such information at school. The main thing to remember is that with a decrease in pressure, the boiling point of the liquid also decreases, and with its increase, 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 in institutes.

One of the important steps for obtaining a tasty, healthy and fragrant infusion is getting boiling water. But remember, boiled water, as well as re-boiled water, is dead water!

Water usually contains a lot of microscopic salts, and if it is boiled, their concentration will increase. Boiling water must be young. If the water does not have time to boil, the tea leaves will not unroll, will not fall to the bottom, but will float on the surface. The tea will not brew and the aroma of the tea will not be revealed either. And each tea has its own temperature requirements. So after the water has boiled, if a temperature lower than 100 degrees is needed, it is allowed to cool. When there is no water thermometer at hand, they use the rule that water cools down to about 85 degrees in five minutes.

To get young boiling water, you need to monitor the water in the kettle. In the treatise of the famous Lu Yu, it was said that when the "crab eye" first appears - small bubbles at the bottom and at the same time a slight clicking begins - this is the first stage of boiling water. The water temperature is about 70-80 C.

Then the bubbles increase, the crackling becomes more frequent and merges into a slight noise and the second short stage called the "fisheye" begins. The temperature is about 80-85C.

Then "pearl threads" begin to rise along the walls of the teapot - sort of strings of bubbles, the water begins to boil, the noise changes a little and becomes, as it were, muffled - this is the third stage. It is she who is considered the most suitable for pouring tea into water (if you brew tea using the Lu Yu method) or removing water from the fire. The temperature is about 85-92C. Also behind this stage there is a very short one - this stage is called "Wind noise in the pines" - if you listen to the water at this moment, you will understand why. But since you need to practice to catch it, we recommend that you shoot the kettle not at the third stage.

When stormy waves go over the surface of the water - the so-called "bulk boiling" - this is the fourth stage of boiling water brewing. The fourth stage of boiling water, according to Lu Yu, is not suitable for brewing tea. And the thing is that the oxygen contained in the water is lost, they leave the water with steam, from which the water changes its taste.

If the water is hard or not clean, then there will be no classic boiling stages or they will be smeared.

The water boiled, and we got young boiling water. Then, if necessary, let the water cool down. If we don’t remember what temperature was recommended in the description for tea, then we adhere to the general rule:

Water temperature from 90 degrees to 95 is suitable for brewing black teas, for example pu-erh, fully fermented(these are red teas) and also highly fermented oolong teas.

Water temperature from 80 to 90 degrees is brewed mainly lightly fermented Taiwanese oolong teas.

Low water temperature, which is below 80 degrees, suitable for green, white and yellow teas.

The importance of making tea desired temperature, because if you brew tender green or white tea with boiling water, then there will be no freshness, there will be no lightness, there will be no sweetness, there will be no rich aftertaste, but there will be a taste of bitterness and unpleasant astringency. Only properly brewed tea will give us amazing sensations, feelings of pleasant lightness, purity of thought and, finally, pleasant communication, if brewed not only for ourselves.

Happy tea!