We explain what evaporation is and what it consists of, with examples. Also, how it intervenes in the water cycle and its difference with boiling.
What is evaporation?
Evaporation is a physical process that consists of the transformation of a substance from a liquid state to a gaseous state. It is a process that occurs on the surface of the liquid, at any temperature, and slowly and gradually.
Although evaporation of a liquid can occur at any temperature, if the temperature of the liquid is increased, the faster evaporation occurs.
Evaporation is of vital importance to sustain life on planet Earth, as it is one of the stages of the water cycle, which is a biogeochemical cycle through which water moves from one region to another, ensuring that all living beings they can consume it.
See also: Physical phenomena
What is the evaporation process?
The evaporation process begins when the molecules that are located on the surface of the liquid move in the appropriate direction and with sufficient kinetic energy to overcome the molecular forces that hold them together in the liquid phase.
Kinetic energy is the energy that a body (in this case, water molecules) acquires due to its relative motion. When the temperature increases, the kinetic energy increases. That's why, As the temperature of water increases, the kinetic energy of its molecules increases. and this makes it possible for the water molecules to separate.
This occurs because once the molecules that are located on the surface of the liquid have enough energy, overcome the molecular forces of attraction, separate and pass into the gas phase.
See also: Physical change
Types of evaporation
The evaporation process occurs spontaneously in nature by increasing the temperature of a liquid, but it can also be generated in a laboratory by human action. In this sense, two types of evaporation can be defined:
- Natural evaporation It occurs in nature, without the influence of man. An example of natural evaporation is the evaporation of water from a lake when its temperature increases due to heating caused by the sun.
- Assisted evaporation It is generated by humans in a laboratory. It can be used as a method to separate the components of a solution or mixture.
Examples of evaporation
Some examples in which you can see the evaporation process:
- The drying of wet clothes placed in the sun, when water evaporates on its surface.
- The natural drying of wet hair after a bath.
- The gradual disappearance of sweat after exercising.
- The evaporation of water from rivers and seas.
- The gradual drying of the floor after it has been mopped and scrubbed with water.
- Obtaining sea salt from the evaporation of seawater in a salt pan.
- The reduction and disappearance of the puddles that form with the rain, once it ends and the sun rises.
- The drying of the dew drops that appear on the leaves of the plants in the morning.
- Evaporation of water in dog and cat bowls.
- Evaporation of water in a vase with flowers.
Differences between vaporization, evaporation and boiling
It is called Vaporization is the process of changing a substance from a liquid state to a gaseous state.
Vaporization can occur through two processes:
- Evaporation which is the passage of a substance from the liquid state to the gaseous state, and occurs gradually at the surface of the liquid and at any temperature.
- The boiling which is the passage of a substance from the liquid state to the gaseous state, and occurs when the temperature of the total mass of the liquid is greater than its boiling point.
The boiling point of a liquid substance is the temperature at which its vapor pressure equals the pressure surrounding it. If the vapor pressure of the liquid is equal to the atmospheric pressure (1 atm), then it is called normal boiling point. The boiling point is specific for each substance.
Evaporation in the water cycle
The water cycle or hydrological cycle is the process by which water circulates above and below the solid surface of the earth.
During this cycle, water moves from one region to another and also changes its state of aggregation, that is, it transforms from liquid to solid, from solid to liquid, from liquid to gaseous, from gaseous to liquid, from solid to gaseous and from gaseous to solid.
Evaporation is one of the stages of the water cycle which begins when the water on the Earth's surface evaporates. Subsequently, the water vapor rises (mixed with air) until it cools, condenses and forms clouds (this stage is known as “condensation”).
If the climate is warm, the water condensed in the clouds falls in the form of droplets to the Earth's surface, which is known as rain or precipitation. If the weather is cold, water can fall as hail or snow.
Evaporation is a very important stage of the water cycle, as it ensures that the necessary levels of humidity are maintained in the air to sustain life on the planet.
Evaporation as a method of separation of mixtures
The evaporation process can be used as a method to separate mixture components (combination of two or more components without involving chemical bonds between them) or dissolution (a homogeneous mixture).
Some techniques to achieve evaporation of a component and separate it from the rest are:
Evaporation by increasing the temperature of the mixture
It consists of heating a mixture (usually a solid-liquid mixture) until the molecules of the liquid acquire enough energy to separate from the surface of the liquid and pass into the gas phase. The molecules of the solid component remain in the container.
This procedure is used to separate mixtures that preferably do not contain flammable solvents. It is also used to dry solids.
Evaporation by decreasing the pressure surrounding the mixture
It consists of reducing the pressure surrounding a mixture (solid-liquid mixture in this case), which causes the molecules of the liquid to separate are released (due to the low pressure on them) and pass into the gas phase. The molecules of the solid component remain in the container.
This process is usually carried out at room temperature (25 ⁰C), and is used to dry substances that are unstable at high temperatures.
Evaporation by combining the increase in temperature and decrease in pressure
It consists of combine the two previous procedures to separate mixtures made up of components with certain instability at elevated temperatures.
An example of the application of evaporation as a method of separating mixtures can be seen in salt flats, which are places where the sun heats seawater until the water passes into the gaseous state and the solid salt remains at the bottom. of large deposits.
References
- Manzur, A., & Cardoso, J. (2015). Mexican journal of physics E, 61(1), 31-34.
- Fiedler, R. (1955, June). The importance of the solar evaporation process for the Saltpeter industry. In Annals of the Institute of Engineers of Chile (No. 9-10, pp. page-397).
- Peter Atkins,Loretta Jones (2012). Principles of chemistry The paths of discovery. Panamericana Medical Editorial. ISBN: 09789500602822
