Evaporation is... a Process of phase transition of a substance from liquid to vapor

In the world around us constantly and continuously, there is a huge variety of physical phenomena and processes. One of the most important can be considered the process of evaporation. There are several required conditions for this phenomenon. In this article we will examine each of these in more detail.

What is vaporization?

Is the process of transforming substances in a gaseous or vapor state. It is characteristic only of the substances is a liquid consistency. However, something similar is observed in solids, called the phenomenon of sublimation. This can be seen with careful monitoring bodies. For example, a piece of soap over time dries and starts to crack, this is because droplets of water in its structure evaporates and transition to a gas phase H₂O.

Definition in physics

Evaporation is an endothermic process in which the source of energy that is absorbed is the heat of phase transition. It includes two components:

• A certain amount of heat is required to overcome molecular forces of attraction, when there is a gap between the connected molecules;
• The heat needed for the expansion of the molecules in the process of turning liquids into vapor or gas.

How does it happen?

The Transition of a substance from liquid to gaseous state may occur in two ways:

1. Evaporation is the process in which the surface of the liquid substance to volatilize the molecules.
2. Boil - the process of vaporization of the liquid by bringing the temperature to a specific heat of boiling of the substance.

Despite the fact that both of these phenomena transform the liquid substance into a gas, between them there are significant differences. Boiling is an active process that occurs only at a certain temperature, while evaporation occurs at all conditions. Another difference is that the boiling characteristic of the entire thickness of the liquid, and the latter only occurs on the surface of liquids.

Recommended

"Knowledge is light and ignorance is darkness": the value, meaning and alternatives

There are some sayings that would seem to need no explanation, such as “teaching & ndash; light and ignorance – darkness”. But some still do not understand their meaning. But not only for such people is written by our article. I...

What was invented by Mendeleev for the army. The history and fate of the invention

D. I. Mendeleev was a brilliant Russian scientist-polymath, who made many important discoveries in various fields of science and technology. Many people know that he is the author of “Fundamentals of chemistry" and the periodic law of chem...

The origin of the Slavs. The influence of different cultures

Slavs (under this name), according to some researchers, appeared in the story only in 6 century ad. However, the language of nationality bears the archaic features of the Indo-European community. This, in turn, suggests that the origin of the Slavs h...

Molecular-kinetic theory of evaporation

If we consider this process at the molecular level, it is as follows:

1. The Molecules in liquid substances, are in constant chaotic motion, all of them have completely different speeds. Meanwhile, particles are attracted to each other due to the force of gravity. Each time they collide, their velocities change. At some point, some developing very high speed, allowing to overcome the force of gravity.
2. Those elements that appeared on the surface of the liquid possess kinetic energy that can overcome the intermolecular connection, and leave the liquid.
3. These are the fastest molecules emitted from the surface of the liquid substance, and this process occurs constantly and continuously.
4. Once airborne, they turn into steam - it is called evaporation.
5. As a result, the average kinetic energy of the remaining particles becomes smaller. This explains the cooling fluid. Remember how in the childhood we were taught to blow on the hot liquid that she would rather cold. It turns out that we accelerate the process of evaporation of water, and the temperature drop is much faster.

What factors depend on?

There are many conditions necessary for the occurrence of this process. It occurs everywhere where there are particles of water: lake, sea, river, all wet items, covers the bodies of animals and people, as well as the leaves of plants. It can be concluded that the evaporation is very important and essential process to the outside world and all living beings.

So what factors affect this phenomenon:

1. The evaporation Rate depends on the composition of the fluid itself. It is known that each of them has its own peculiarities. For example, those substances which have a heat of vaporization below, will be converted faster. Compare the two processes: evaporation of alcohol and water. In the first case, the conversion to gaseous state takes place faster because the latent heat of vaporization and condensation of alcohol is equal to 837 kJ/kg and the water is almost three times more - 2260 kJ/kg.
2. The Speed also depends on the initial temperature of the liquid: the larger it is, the faster it produces steam. As an example, take a glass of water when inside of vessel is boiling, vaporization occurs at a far greater rate than when the temperature of the water below.
3. Another factor that determines the speed of the flow of this process is the surface area of the liquid. Remember that in the plate of large diameter hot soup cools down faster than in a small saucer.
4. The Speed of propagation of substances in the ambient air largely determines the evaporation rate, i.e. the faster diffusion occurs, the more evaporation occurs. For example, in strong winds the drops of water quickly evaporate from the surface of lakes, rivers and reservoirs.
5. The temperature of the air in the room also plays an important role. Read more about it we'll talk later.

What is the role of humidity?

Due tothe fact that the evaporation process occurs continuously and constantly everywhere, in the air there are always water particles. In molecular form they look like a group of elements H₂O. the Liquid can evaporate, depending on the indicator of the amount of water vapor in the atmosphere, this ratio is called humidity. It is of two types:

1. Relative humidity is the ratio of the amount of water vapor in the air to the density of saturated steam at the same temperature in percentage. For example, the rate of 100% indicates that the atmosphere is fully saturated with molecules of H₂O.
2. Absolute characterizes the density of water vapor in the air is indicated by the letter f and shows what a mass of water molecules contained in a 1m³ of air.

The Relationship of the evaporation and the humidity of the air may be determined in the following way. The lower the figure the relative humidity, the faster will be the evaporation from the surface of the earth and other objects.

Evaporation of various substances

Various substances this process occurs in different ways. For example, the evaporation of the alcohol is faster than that of other liquids due to its small specific heat of vaporization. Often, such liquids are called volatile, because water vapor is literally seeping out of them virtually at any temperature.

Alcohol may also evaporate, even at room temperature. In the process of cooking wine or vodka, the alcohol is passed through the still, just reaching the boiling point, it is roughly 78 degrees. However, the actual temperature of evaporation of the alcohol will be a little bit more because in the original product (e.g. Braga) it is a compound with various aromatic oils and water.

Condensation and sublimation

The Following phenomenon can be observed every time the water begins to boil in the kettle. Please note that when boiling water goes from a liquid to gaseous state. It happens this way: hot water vapor jet high speed fly out of the kettle through the spout. In this case the resulting steam can be seen right at the exit of the nozzle, and at a small distance from him. This process is called condensation, i.e., water vapor condensed to such a degree that they become visible to our eyes.

The Evaporation of a solid body is called sublimation. They are moving from one aggregate state to gaseous, skipping the liquid stage. The most famous case of sublimation is associated with the ice crystals. In its original form ice is a solid at temperatures above 0° it starts to melt, while the liquid state. However, in some cases at low temperatures the ice goes into vapor form without passing through a liquid phase.

The Impact of evaporation on the human body

Evaporation in our body takes place thermoregulation. This process occurs through self-cooling. On a hot hot day to a person who is engaged in a specific physical labor, it becomes very hot. This means that it increases the internal energy. And as you know, at temperatures above 42° protein in human blood begins to clot, if time does not stop this process, it will lead to death.

- cooling is arranged in such a way as to regulate the temperature for normal functioning. When the temperature becomes the upper limit, the pores on the skin started sweating. And then from the skin surface evaporation, which absorbs the excess energy of the body. In other words, evaporation is a process that promotes cooling of the body to a normal state.