What is boiling, it is known from the school curriculum. Nevertheless, this knowledge quickly disappears, and gradually people stop paying attention to the essence of habitual phenomena. It is sometimes useful to recall theoretical knowledge.
Definition
What is boiling? This is a physical process during which intense 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 are composed of saturated steam and air.
It is worth noting the existence of such a thing as boiling point. The rate of vapor formation also depends on pressure. It must be permanent. Typically, the main characteristic of liquid chemicals is the boiling point at normal atmospheric pressure. Nevertheless , factors such as the intensity of sound waves and air ionization can also influence this process.
Stage boiling water
Certainly, steam begins to form during a procedure such as heating. Boiling involves the passage of liquid through 4 stages:
- Small bubbles begin to form at the bottom of the vessel, as well as on its walls. This is a result of the fact that cracks in the material of which the container is made contain air, which expands under the influence of high temperature.
- Bubbles begin to increase in volume, as a result of which they burst to the surface of the water. If the upper layer of liquid has not yet reached the boiling point, the cavities sink to the bottom, after which they again begin to tend upward. This process leads to the formation of sound waves. That is why during boiling water we can hear a noise.
- The largest number of bubbles floats to the surface, which creates the impression of turbidity of water. After that, the liquid turns pale. Given the visual effect, this boiling stage is called the "white key."
- Intense drilling is observed, which is accompanied by the formation of large bubbles that burst quickly. This process is accompanied by the appearance of splashes, as well as intense steam formation.
Specific heat of vaporization
Almost daily we encounter such a thing as boiling. The specific heat of vaporization is a physical quantity that determines the amount of heat. With its help, a liquid substance can be converted into steam. In order to calculate this parameter, it is necessary to divide the rate of heat of evaporation by mass.
How is the measurement
The specific heat of formation is measured in laboratory conditions by conducting appropriate experiments. They include the following actions:
- the necessary amount of liquid is measured, which is then poured into the calorimeter;
- initial measurement of water temperature;
- a flask is installed on the burner with the test substance previously placed in it;
- the steam released by the test substance is launched into the calorimeter;
- repeated measurement of water temperature;
- the calorimeter is weighed, which allows you to calculate the mass of condensed vapor.
Bubble Boil
Dealing with the question of what is boiling, 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 boiling mode is called bubble. Typically, cavities filled with steam are formed precisely 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 without reaching large sizes.
Film boil
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 regime, a film is also isolated. Its essence lies in the fact that with increasing heat flux, 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 is characterized in that the degree of heat transfer from the walls of the vessel to the liquid itself is significantly reduced. The reason for this is the same steam film.
Boiling temperature
It should be noted that there is a dependence of the boiling point on the pressure that is on the surface of the heated fluid. So, it is generally accepted that water boils when heated to 100 degrees Celsius. Nevertheless, this indicator can be considered fair only if the atmospheric pressure indicator is considered normal (101 kPa). If it will increase, the boiling point will also change in the direction of increase. So, for example, in popular pressure cooker pans, 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 be considered mountainous 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 cooking. So, for example, to boil an egg, you will have to heat the water no less than 100 degrees, otherwise the protein will not coagulate.
Boiling of a substance depends on the saturated vapor pressure index. 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 only 114 Pa (for water this indicator is 101 325 Pa).
Boiling in different conditions
Depending on the conditions and condition of the liquid, the boiling point may vary significantly. For example, you should add salt to the liquid. Chlorine and sodium ions are placed between water molecules. Thus, boiling requires an order of magnitude more energy, and, accordingly, time. In addition, such water forms much less steam.
The kettle is used for boiling water in a domestic environment. If pure liquid is used, then the temperature of this process is standard 100 degrees. Under similar conditions, distilled water boils. Nevertheless, a little less time will be spent, given the absence of impurities.
What is the difference between boiling and evaporation?
Whenever boiling water occurs, steam is released into the atmosphere. But these two processes cannot be equated. They are only methods of vaporization that occurs under certain conditions. So, boiling is a first- order phase transition . This process is more intense than evaporation. This is due to the formation of steam foci. It is also worth noting that the evaporation process occurs exclusively on the surface of the water. Boiling also applies to the entire volume of liquid.
What evaporation depends on
Evaporation is the process of converting a liquid or solid into a gaseous state. There is an “outburst” of atoms and molecules, the bond of which with the rest of the particles is weakened under the influence of certain conditions. Evaporation rate may vary due to the following factors:
- liquid surface area;
- temperature of the substance itself, as well as the environment;
- molecular velocity;
- type of substance.
Interesting facts about boiling
The boiling energy of water is widely used by humans in everyday life. This process has become so routine and familiar that no one thinks about its nature and features. Nevertheless, a number of interesting facts are associated with boiling:
- Probably everyone noticed that there is a hole in the lid of the kettle, but few people think about its purpose. It is done with the aim of partially releasing steam. Otherwise, water may splash through the spout.
- The duration of cooking potatoes, eggs and other food products does not depend on how powerful the heater is. The only fact that matters is how long they have been exposed to boiling water.
- A boiling point such as this is not affected by the power of the heater. It can only affect the rate of evaporation of the liquid.
- Boiling is associated not only with heating water. Using this process, you can also make the liquid freeze. So, in the process of boiling, it is necessary to continuously pump air from the vessel.
- One of the most pressing problems for housewives is that milk can "run away." Thus, the risk of this phenomenon increases significantly during worsening weather, which is accompanied by a drop in atmospheric pressure.
- The hottest boiling water is obtained in deep underground mines.
- Through experimental studies, scientists were able to establish that on Mars, water boils at a temperature of 45 degrees Celsius.
Can water boil at room temperature?
Through simple calculations, scientists were able to establish that water can boil at room temperature at the level of the stratosphere. Similar conditions can be recreated using a vacuum pump. Nevertheless, a similar experiment can be conducted in simpler, mundane conditions.
In a liter flask, you need to boil 200 ml of water, and when the container is filled with steam, it must be tightly closed, removed from heat. Having placed it over the crystallizer, you need to wait until the end of the boiling process. Next, the flask is doused with cold water. After that, intense boiling will begin again in the container. This is due to the fact that under the influence of low temperature the steam located in the upper part of the flask is lowered.