Evaporation

EVAPORATION

We explain what evaporation is, how it intervenes in the water cycle and how it is used as a method of separating mixtures.

What is evaporation?

Evaporation is a physical process that involves the gradual passage of a liquid into the gaseous state. It is a slow and silent transit, which occurs as a result of a temperature increase. The reverse process is known as condensation (transition from gas to liquid).

As a result of the heat, the molecules of the liquid are agitated and acquire the energy necessary to get rid of the liquid and transform into steam.

Evaporation can be observed, for example, in puddles that form after the rain and then evaporate when the sun rises; also in the formation of clouds from the evaporation of the waters of rivers and oceans.

Evaporation

Evaporation and vaporization

evaporation vaporization boiling

When a liquid boils, the change of state affects its entire mass.

Both evaporation and vaporization are processes of transformation from liquid to gaseous state. When it occurs only on the surface of the liquid, it is called evaporation. If the process affects the entire liquid mass, it is called vaporization or boiling.

Evaporation is a process that is generated with temperature increases below the boiling point. If the process occurs from the boiling point, it is vaporization: a rapid and violent process that occurs throughout the liquid mass.

The boiling point is reached when the vapor pressure of a liquid equals the surrounding atmospheric pressure. When this pressure level is reached, the liquid begins to boil and its molecules assume a gaseous state. Each liquid has a different boiling point. In the case of water, the boiling point is 100º C.

Examples of evaporation

Some examples of this process of transformation from liquid to gaseous state:

Drying wet clothes sunset.

Natural drying of wet hair after a bath or getting wet with rain.

The gradual disappearance of the sweat of our bodies, after working or exercising.

The formation of clouds over the waters of rivers and oceans.

Gradual drying of the soil after being mopped and scrubbed with water.

Obtaining sea salt from the evaporation of seawater in a saline.

The reduction and disappearance of the puddles that form with the rain, once it ends and the sun rises.

Evaporation and water cycle

evaporation water cycle clouds

The water cycle describes all the hydrological exchanges that occur between the atmosphere, the earth and the sea through the three states of water: the solid, the liquid and the gas.

The sun evaporates the water on the surface of the seas, lakes and rivers and this vapor, when entering the heights of the atmosphere, condenses transforming itself again into liquid.

This liquid descends to the earth through a phenomenon known as precipitation that, in cold climates, can occur in a solid state of water such as snow or hail. In hot weather climates will produce liquid precipitation in the form of rain.

From the water cycle we can deduce the enormous importance of solar evaporation from the waters of the planet, which helps produce the climate and renews the humidity of the air and vegetation. Without this evaporation process, life on Earth would not be possible.

Evaporation as a method of separation

In chemical science, evaporation has been incorporated as a basic and very efficient method to separate a solution or mixture in which a solute and a solvent are found.

The process is carried out by heating the solution until the solvent evaporates and leaves a solid residue. Naturally, this occurs with sea salt when the sun separates the water from the salt crystals at the seashore.

We can reproduce this separation process through a simple experiment, using a mixture of salt and water. To separate salt from salt water, the solution is heated in a beaker. While the water boils, we see how it escapes in the form of steam until it disappears completely leaving only a layer of salt.