Evaporation is the transition from a liquid to a gaseous state. It occurs on the free surface of liquids, slowly and gradually, at any temperature.
A substance when in a liquid state has less cohesive force between its atoms than when it is in a solid state.
In this state, the molecules are further apart, in constant agitation and move within the liquid at different speeds.
In this way, the particles with greater speed, when reaching the free surface of the liquid, manage to escape passing into the gaseous state.
Evaporation Speed
There are factors that influence the speed at which evaporation occurs, they are:
- Temperature : the higher the temperature, the faster the evaporation speed. Because the higher the temperature, the greater the kinetic energy of the particles. In this way, more particles will escape from the liquid’s surface.
- Nature of the liquid : there are substances that evaporate more easily, they are called volatile substances. Ether, alcohol and acetone are examples of volatile substances.
- Free surface area : since evaporation occurs on the free surface of liquids, the larger the surface, the greater the amount of particles that will leave the liquid.
- Concentration of vapor on the liquid : the greater the amount of vapor, the lower the evaporation speed.
- Pressure on the liquid : the higher the pressure, the lower the evaporation speed.
Difference between Evaporation and Boiling
Both evaporation and boiling represent a change from a liquid to a gaseous state. However, while evaporation occurs gradually, boiling occurs quickly.
For boiling to occur, it is necessary for the liquid to reach, for a given pressure, a certain temperature, called the boiling point. Evaporation can occur at any temperature.
Separation of Mixtures
Fractional crystallization is a process of separating heterogeneous mixtures. It is used when the substances that make up the mixture are in the solid state.
In this process a liquid is added to the mixture that dissolves all the solid components. The components then crystallize separately after the solution has evaporated.
This process is used, for example, in salt pans to obtain salts from sea water.
Evaporation and the Water Cycle
Evaporation is one of the processes that make up the water cycle . The energy from the sun heats the free surface of lakes, rivers, seas and oceans.
This heating causes part of the water to evaporate, changing to a vapor state. This, when reaching the highest layers of the atmosphere, cool and condense forming clouds.
When precipitation occurs, the water returns to the surface in liquid form, infiltrating the soil and forming the underground sheets.
Part of this water is absorbed by the plants, which return the atmosphere to water vapor by transpiration.
Phase changes
The change from a liquid to a gaseous state is generically called vaporization , since it includes, in addition to evaporation, two other processes: boiling and heating.
There are also other processes of change of state. Are they:
- Fusion
- Solidification
- Liquefaction or Condensation
- Sublimation
In the diagram below we represent the three physical states of matter and the respective state changes:
