Что такое кипение, известно еще из школьной programs. Nevertheless, this knowledge quickly disappears, and gradually people stop paying attention to the essence of familiar phenomena. Sometimes it is useful to remember theoretical knowledge.
Definition
What is boiling?This is a physical process during which intensive vaporization occurs both on the free surface of the liquid and inside its structure. One of the signs of boiling is the formation of bubbles, which consist of saturated steam and air.
It is worth noting the existence of such a thing asboiling temperature. The rate of vapor formation also depends on the pressure. It should be permanent. As a rule, the main characteristic of liquid chemicals is the boiling point at normal atmospheric pressure. Nevertheless, factors such as sound wave intensity and air ionization can also affect this process.
Stage boiling water
It certainly begins to form steam during a procedure such as heating. Boiling involves passing the liquid through 4 stages:
- At the bottom of the vessel, as well as on its walls beginsmall bubbles form. This is due to the fact that the cracks in the material from which the container is made contain air, which expands when exposed to high temperature.
- Bubbles begin to increase in volume, inthe result is that they break out onto the surface of the water. If the upper layer of the liquid has not yet reached the boiling point, the cavities sink to the bottom, after which they start to move upward again. This process leads to the formation of sound waves. That is why during the boiling water we can hear the noise.
- The surface floats the mostbubbles, which gives the impression of water turbidity. After that, the liquid turns white. Given the visual effect, this boiling stage is called the "white key".
- There is intense boiling, which is accompanied by the formation of large bubbles, which quickly burst. This process is accompanied by the appearance of splashes, as well as intensive formation of steam.
Specific heat of vaporization
Almost every day we are confronted with sucha boiling phenomenon. The specific heat of vaporization is a physical quantity that determines the amount of heat. With it, the liquid substance can be converted into steam. In order to calculate this parameter, it is necessary to divide the indicator of heat of evaporation into mass.
How is the measurement?
The indicator of the specific heat of formation is measured in the laboratory by conducting appropriate experiments. They include the following actions:
- the required amount of liquid is measured, which is then poured into the calorimeter;
- initial water temperature measurement is performed;
- A flask with a test substance placed in it is placed on the burner;
- the vapor released by the test substance is launched into the calorimeter;
- re-measurement of water temperature;
- the calorimeter is weighed, which makes it possible to calculate the mass of the condensed vapor.
Bubble boiling mode
Determining what boiling is,It is worth noting that it has several modes. So, when heated, steam can form in the form of bubbles. They periodically grow and burst. This mode of boiling is called bubbly. Usually cavities filled with steam are formed just at the walls of the vessel. This is due to the fact that they are usually overheated. This is a necessary condition for boiling, because otherwise the bubbles will collapse, not reaching large sizes.
Film boiling mode
What is boiling?The easiest way to explain this process is as vaporization at a certain temperature and constant pressure. In addition to the bubble mode, emit also film. Its essence lies in the fact that when the heat flow increases, the individual bubbles combine to form a vapor layer on the walls of the vessel. When a critical indicator is reached, they break through to the surface of the water. This boiling mode differs in that the degree of heat transfer from the vessel walls to the liquid itself is significantly reduced. The reason for this is the same steam film.
Boiling temperature
It is worth noting that there is a dependencyboiling point of pressure, which is on the surface of the heated liquid. So, it is considered that water boils when heated to 100 degrees Celsius. Nevertheless, this indicator can be considered fair only if the indicator of atmospheric pressure is considered normal (101 kPa). If it increases, the boiling point also changes upwards. For example, in popular pressure cookers, the pressure is about 200 kPa. Thus, the boiling point rises by 20 points (up to 20 degrees).
An example of low atmospheric pressure can becount mountain areas. So, given that there it is quite small, the water begins to boil at a temperature of about 90 degrees. Residents of such areas have to spend much more time preparing food. So, for example, to boil an egg, it is necessary to heat the water not less than 100 degrees, otherwise the protein will not curdle.
Boiling point depends on the pressuresaturated steam. Its effect on temperature is inversely proportional. For example, mercury boils when heated to 357 degrees Celsius. This can be explained by the fact that the saturated vapor pressure is equal to only 114 Pa (for water, this indicator is 101 325 Pa).
Boiling in different conditions
Depending on the condition and condition of the fluid,boiling point may vary significantly. For example, add salt to a liquid. Chlorine and sodium ions are located between water molecules. Thus, boiling takes an order of magnitude more energy, and accordingly - time. In addition, this water forms a lot less steam.
Kettle is used to boil water in householdconditions. If pure liquid is used, then the temperature of this process is standard 100 degrees. Under similar conditions, distilled water boils. However, it will take a little less time, given the absence of impurities.
What is different from boiling evaporation
Whenever boiling water occurs, steamreleased into the atmosphere. But these two processes cannot be identified. They are only methods of vaporization that occurs under certain conditions. So, boiling is a phase transition of the first kind. This process is more intense than evaporation. This is due to the formation of vapor lesions. It is also worth noting that the evaporation process takes place exclusively on the surface of the water. Boiling concerns the total volume of the liquid.
What does evaporation depend on?
Evaporation is a processconverting a liquid or solid into a gaseous state. Atoms and molecules “fly out”, the connection of which with other particles is weakened under the influence of certain conditions. The rate of evaporation may change under the influence of the following factors:
- surface area of the liquid;
- the temperature of the substance itself, as well as the environment;
- the speed of movement of molecules;
- kind of substance.
Interesting facts about boiling
Boiling energy of water is widely used.man in everyday life. This process has become so mundane and familiar that no one thinks about its nature and features. Nevertheless, a number of interesting facts are connected with boiling:
- Probably everyone noticed that there is a teapot in the lidhole, but few people think about its purpose. It is done in order to partially release steam. Otherwise, water may spill through the spout.
- Duration of cooking potatoes, eggs and otherfood does not depend on how powerful the heater is. All that matters is how long they have been under the influence of boiling water.
- On such an indicator as the boiling point, does not affect the power of the heating device. It can only affect the rate of evaporation of the liquid.
- Boiling is associated not only with heating water. This process can also make the liquid freeze. So, in the process of boiling it is necessary to produce continuous pumping of air from the vessel.
- One of the most pressing problems for hostessesis that milk can "run away." Thus, the risk of this phenomenon increases significantly during weather deterioration, which is accompanied by a drop in atmospheric pressure.
- The hottest boiling water is obtained in deep underground mines.
- By experimental research, scientists were able to establish that on Mars, water boils at a temperature of 45 degrees Celsius.
Can water boil at room temperature?
By simple calculations, scientists have succeededestablish that water can boil at room temperature at the level of the stratosphere. Similar conditions can be recreated with a vacuum pump. Nevertheless, a similar experience can be carried out in more simple, mundane conditions.
In a liter flask you need to boil 200 ml of water, andwhen the tank is filled with steam, it must be tightly closed, removed from the fire. Placing it above the mold, you need to wait for the end of the boiling process. Next, pour the flask with cold water. After that, intensive boiling will begin again in the container. This is due to the fact that under the influence of low temperature, the vapor in the upper part of the flask is lowered.
