CHEMICAL EVAPORATION: WHAT IT CONSISTS OF, APPLICATIONS AND EXAMPLES - CHEMISTRY - 2025

The chemical evaporation is the process by which molecules are separated from a liquid surface and passing the gaseous state. It is a process that absorbs energy, and therefore, it is endothermic. The molecules near the surface of the liquid increase their kinetic energy to evaporate.

As a result of this increase in energy, the intermolecular forces of cohesion or attraction between these molecules weaken and escape from the liquid phase to the gas phase. As there is no boundary where the gaseous molecules revolve to penetrate the liquid again, all this ends up evaporating completely.

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Unlike boiling, evaporation can occur at any temperature before the liquid boils. This phenomenon is then the reason why you can see water vapors emanate from the forests, which when in contact with cold air, condenses micro drops of water giving them a white color.

Condensation is a reverse process that may or may not establish an equilibrium with the evaporation that occurs in the liquid.

There are factors that affect evaporation, such as: the speed of the process or the amount of molecules that can evaporate from a liquid; the nature or type of the liquid; the temperature to which the liquid is exposed, or if it is in a closed or open container exposed to the environment.

Another example of chemical evaporation occurs in our body: when we sweat, part of the liquid in the sweat evaporates. The evaporation of sweat leaves a feeling of cold in the body due to evaporative cooling.

What is evaporation?

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It consists of the capacity or property of the molecules located on the surface of a liquid to transform into vapor. From a thermodynamic point of view, energy absorption is required for evaporation to take place.

Evaporation is a process that occurs in the molecules that are located at the level of the free surface of the liquid. The energetic condition of the molecules that make up the liquid is fundamental for the change from the liquid to the gaseous state to take place.

The kinetic energy or energy that is the product of the movement of the particles of a body, is maximum in the gaseous state.

Cohesion forces

For these molecules to get out of the liquid phase, they must increase their kinetic energy so that they can evaporate. With the increase in kinetic energy, the cohesion force of the molecules near the surface of the liquid decreases.

The cohesion force is one that exerts molecular attraction, which helps to hold molecules together. Evaporation requires a contribution of energy provided by the particles of the surrounding medium to reduce this force.

The inverse process of evaporation is called condensation: the molecules that are in the gaseous state return to the liquid phase. It occurs when molecules in the gaseous state collide with the surface of the liquid and become trapped in the liquid again.

Both evaporation, viscosity, surface tension, among other chemical properties, are different for each of the liquids. Chemical evaporation is a process that will depend on the type of liquid among other factors that are detailed in the next section.

Factors involved in chemical evaporation

There are numerous factors that influence the evaporation process, favoring or inhibiting this process. There is the type of liquid, the temperature, the presence of air currents, the humidity, among many other factors.

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Each type of liquid will have its own cohesive or attractive force that exists between the molecules that compose it. In oily fluids such as oil, evaporation generally occurs to a lesser extent than in those aqueous liquids.

For example, in water the cohesion forces are represented by the hydrogen bonds that are established between its molecules. The H and O atoms that make up a water molecule are held together by polar covalent bonds.

Oxygen is more electronegative than hydrogen, which makes it easier for a water molecule to hydrogen bond with other molecules.

Temperature

Temperature is a factor that affects the kinetic energy of the molecules that are forming liquids and gases. There is a minimum kinetic energy required for molecules to escape from the surface of the liquid.

At low temperature, the portion of molecules in the liquid that have enough kinetic energy to evaporate is small. That is, at low temperature the evaporation of the liquid will be less; and therefore, evaporation will be slower.

Rather, evaporation will increase as the temperature increases. As the temperature increases, the proportion of molecules in the liquid that acquire the kinetic energy necessary to evaporate will also increase.

Closed or open container

Chemical evaporation will be different depending on whether the container where the liquid is located is closed or open exposed to air.

If the liquid is in a closed container, the evaporating molecules quickly return to the liquid; that is, they condense when they collide with a physical border, such as walls or a lid.

A dynamic equilibrium is established in this closed container between the evaporation process that the liquid undergoes with that of condensation.

If the container is open, the liquid can evaporate continuously even to its entirety depending on the time of exposure to air. In an open container there is no opportunity for a balance to be established between evaporation and condensation.

When the container is open, the liquid is exposed to an environment that facilitates the diffusion of the evaporated molecules. Furthermore, the air currents displace the evaporated molecules, replacing them with other gases (mostly nitrogen and oxygen).

Concentration of evaporated molecules

The concentration that exists in the gas phase of the evaporating molecules is also decisive. This evaporation process will decrease when there is a high concentration of the evaporating substance in the air or environment.

Also when there is a high concentration of different evaporated substances in the air, the evaporation rate of any other substance decreases.

This concentration of evaporated substances occurs mainly in those cases in which there is no adequate recirculation of air.

Pressure and surface area of ​​the liquid

If there is less pressure on the molecules on the surface of the liquid, the evaporation of these molecules will be more favored. The wider the surface area of ​​the liquid exposed to air, the more rapid evaporation will occur.

Applications

Evaporative cooling

It is already clear that only the liquid molecules that increase their kinetic energy change their liquid phase to the gaseous one . Simultaneously, in the molecules of the liquid that do not escape, there is a decrease in kinetic energy with a decrease in temperature.

The temperature of the liquid that is still conserved in this phase drops, it cools; This process is called evaporative cooling. This phenomenon explains why the liquid without evaporating when it cools can absorb heat from the environment that surrounds it.

As mentioned above, this process allows us to regulate our body's body temperature. Also this evaporative cooling process is used for the cooling of environments through the use of evaporative coolers.

Materials drying

-Evaporation at an industrial level is used for drying various materials made with cloth, paper, wood, among others.

-The evaporation process also serves to separate solutes such as salts, minerals, among other solutes from liquid solutions.

-Evaporation is used to dry objects, samples.

-Allows the recovery of many substances or chemicals.

Drying of substances

This process is essential for the drying of substances in a large number of biomedical and research laboratories in general.

There are centrifugal and rotary evaporators that are used to maximize solvent removal from multiple substances at once. In these devices or special equipment, the samples are concentrated and slowly subjected to a vacuum to the evaporation process.

Examples

-An example of chemical evaporation occurs in the human body when the process of sweating occurs. When sweating, sweat evaporates, the body tends to cool down and there is a decrease in body temperature.

This process of evaporation of sweat and subsequent body cooling, contributes to the regulation of the body's temperature.

-The drying of clothes is also carried out thanks to the process of water evaporation. Clothes are laid out so that the air current displaces the gaseous molecules and thus there is more evaporation. The temperature or heat of the environment and the atmospheric pressure also influence here.

-In the production of freeze-dried products that are stored and sold dry, such as powdered milk, medicines, among others, evaporation also occurs. However, this evaporation is carried out under vacuum and not due to an increase in temperature.

Other examples.

References

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2. Jimenez, V. and Macarulla, J. (1984). Physiological Physicochemistry. (6 ^ta. Ed). Madrid: Interamericana
3. Whitten, K., Davis, R., Peck M. and Stanley, G. (2008). Chemistry. (8 ^ava. Ed). CENGAGE Learning: Mexico.
4. Wikipedia. (2018). Evaporation. Recovered from:
5. Fennel J. (2018). What is Evaporation? - Definition & Examples. Study. Recovered from: study.com
6. Malesky, Mallory. (April 16, 2018). Examples of Evaporation and Distillation. Sciencing. Recovered from: sciencing.com