Tabla de Contenidos
Evaporation and condensation are part of the natural water cycle. They are physical processes due to which this substance changes state: from liquid to gaseous and from gaseous to liquid. The sun heats the water and evaporates it, turning it into steam. Air currents carry the vapor to the atmosphere, where there is a lower temperature. This causes the condensation of water vapor and the formation of clouds. Cloud particles come into contact and fall as precipitation, which can be rain, snow, or hail.
Later, the water falling in the precipitations become part of groundwater, lakes, and rivers, which flow into the seas and oceans, from which the cycle begins again.
However, the processes of evaporation and condensation also occur artificially, in laboratories and industry. These two processes not only occur with water, but also with other substances.
what is evaporation
In addition to being a process that is part of the water cycle, evaporation implies a transition in which a substance that is in a liquid state passes into a gaseous state. This is done only at the surface between the liquid and the gas. Evaporation is the opposite process of condensation.
Evaporation differs from boiling because, as mentioned above, it is a process that occurs on the surface, and not within the liquid. This is an endothermic process because it requires heat to achieve the phase change. Heat is necessary to overcome the forces of molecular cohesion that characterize the liquid state. It is also important during its expansion, when the liquid is vaporizing.
Evaporation is also a method used to separate the components of solid or liquid mixtures. As the temperature increases, the molecules of liquid substances become gaseous and are lost in the air. The other components remain in the container.
Likewise, evaporation can also be defined as a “cooling process”. This is because it removes heat from the surrounding air. A clear example of this is human sweat, which “cools” the body thanks to its evaporation to maintain body temperature.
How does evaporation happen
In order for water molecules to go from a liquid state to a gaseous state, they must gain heat energy. They do this by colliding with other water molecules. Therefore, the evaporation process is closely related to the movement of molecules and the increase in temperature. If there is a higher temperature, the molecules move faster and evaporation occurs more quickly. This is also influenced by the speed of diffusion of the substance. For example, acetone evaporates much faster than water.
When water molecules reach 100 degrees Celsius, they have the necessary kinetic energy to become a gas. But even at lower temperatures, some particles on the surface may have enough energy to overcome the forces of the liquid state and evaporate.
The higher the temperature of the water, the greater the probability that there will be particles with enough kinetic energy to evaporate. For this reason, solar radiation facilitates this process, since it provides energy to the particles. In fact, the particles that evaporate are those with the highest energy. Due to this, the rest of the particles lose energy and thus their temperature is reduced. This is the reason for the cooling of a botijo under the sun.
Other important factors also intervene in the speed of evaporation: pressure, air humidity, wind and the surface where the liquid is located. Evaporation will occur faster from a small area than from a larger one.
Also, not all liquids evaporate at the same rate, as is the case with alcohol or common cooking oil. The evaporation rate will depend on the properties of each substance and the conditions to which it is exposed.
Examples of evaporation
There are numerous examples of evaporation. Some of them are:
- The formation of clouds: the sun heats the sea water and the vapor of water that evaporates rises pushed by the currents of hot air and forms clouds.
- Wet clothes that are dried after hanging: the higher temperature when hanging the clothes in the sun, using a dryer or bringing them closer to a heater, allows the evaporation of the water that impregnates the clothes.
- The steam that comes out of a saucepan when cooking: it is produced when the water begins to boil.
- The evaporation of alcohol at room temperature: due to the high diffusion of this substance.
- Smoke from a hot cup of coffee.
- The wet soil that dries up.
- The disappearance of the puddles that are formed by the rain.
- Body sweat.
- The evaporation of salty sea water, thanks to which sea salt is obtained.
- The water cycle: Evaporation is an important part of the water cycle in nature. When the water particles receive enough heat energy, they evaporate. They then fall as precipitation and eventually return to the sea.
what is condensation
Condensation is the opposite process to evaporation because it allows the transition of water from the gaseous state to the liquid phase. This occurs when the water vapor pressure is greater than the saturation vapor pressure.
It can also be referred to as a “heating process”. Although when water evaporates, cooling must occur for it to condense, heat is released into the surrounding air.
A very common example of condensation in nature is dew, which is water vapor that, when the temperature drops at dawn, condenses and falls on the surface.
The condensation process depends on the pressure, temperature and saturation of the air. When the temperature decreases to “dew point”, the kinetic energy of the molecules is reduced and this facilitates condensation.
How condensation occurs
For condensation to occur, water must lose kinetic energy (the energy of motion). The water vapor particles have a great energy between their molecules and this causes a lot of movement between them, allowing them to distance themselves. When this energy is lost, either due to loss of thermal energy, or due to a change in pressure, the water molecules slow down and move closer, becoming a liquid.
The amount of water vapor in an air mass is called “absolute humidity.” Instead, the amount of water vapor that air mass contains compared to the total amount of vapor that it can accumulate is the “relative humidity.” The dew point is reached when the air becomes saturated, that is, when there is a relative humidity of 100%. This of course varies depending on pressure and temperature. The higher the relative humidity, the higher the rate of condensation of vapor in an air mass.
Examples of condensation
Some common examples of condensation are:
- Dew: the drop in temperature that occurs during the early morning facilitates the condensation of water vapor present in the air and is deposited in the form of droplets on surfaces. When the temperature rises with sunrise, the dew evaporates and the cycle of evaporation and condensation begins again.
- Fog: Fog banks are suspended water particles that condense when they come into contact with cooler surfaces, such as window panes.
- The rain: when the clouds collide, the precipitation of the water particles that condensed occurs, thus forming the rain.
- Droplets of water that appear in cold drinks: the surface of a cold can has a lower temperature than the environment, therefore it receives moisture from the surrounding air, which condenses to form water droplets.
- The water released by air conditioning units: because they absorb moisture from the air, which is at a much lower temperature than outside, and condense it.
- A mirror that fogs up: when taking a hot shower, water vapor adheres to the coldest surfaces and condenses, fogging up mirrors and other objects.
- Diving goggles fogging: the air between the glass of the diving goggles and our face contains water vapor that in turn comes from perspiration. Being in the water, whose temperature is lower than that of the air, the water vapor condenses and fogs the glass of the glasses.
- Breathing: if we breathe near a piece of glass or in a place where there is a low temperature and a lot of humidity, we will see the water vapor as small drops or a whitish vapor. This occurs because the air in our lungs has a higher temperature than the surface or the outside environment. Therefore, it condenses and becomes visible.
- The Water Cycle: Like evaporation, condensation is an essential part of the water cycle. The water vapor rises to the upper layers of the atmosphere, where there are currents of cold air. There it condenses in the form of clouds that precipitate in a liquid state as rain.
Uses and applications of evaporation and condensation
Both evaporation and condensation favor the performance of other processes, especially in the field of science, industry and engineering.
evaporation applications
By means of evaporators designed to facilitate the evaporation process, numerous industrial activities are carried out.
One of them is the production of dairy products. Here, evaporation is used to produce milk, condensed milk, milk proteins, wheys, and other products.
It is also used to produce soy milk and fruit juices; extracts of coffee, tea, malt, yeast; hydrolyzed products such as glucose syrup, or hydrolyzed protein.
In the refrigeration industry it is used to form extracts of meat, bones and blood plasma. In the poultry industry, the evaporation process is essential to produce concentrations of whole eggs or egg whites.
condensation applications
Condensation is essential to carry out distillation, a very important process in laboratories and in industry.
Water can be obtained from condensation, and for this reason, dew collector equipment is used, which collects moisture from the air. In this way, the humidity of the earth is used in desert or semi-arid areas.
Condensation is also useful for obtaining chemicals. It is used as a method to transform some gases that are obtained in chemical reactions into liquids. In this way, its dispersion in the atmosphere is avoided.
Condensers are used in industry to cool and condense the gases that pass through them.
At home, capacitors are used in refrigerators or fridges. They are also used in the manufacture of fire extinguishers. These store condensed carbon dioxide at high pressure.
Bibliography
- Various authors. Physics and chemistry. (2015). Spain. Santillana Education.
- Collective work edebé. Physics and Chemistry . (2015). Spain. Edebé.
- Various authors. The physics book. (2020). Spain. Editorial Akal.
