Table of Contents
Evaporation and Condensation
Evaporation is the process by which water transforms into a vapour. Condensation is the inverse process that converts water vapour to tiny droplets of water. Before reaching its boiling point, a liquid evaporates. Condensation is a phase change that occurs regardless of temperature. This article discusses Evaporation and Condensation which is useful for competitive exams such as the UPSC exam.
Evaporation Definition
Evaporation mainly happens because of temperature. It is the process that turns liquid water into gas (water vapor). The temperature at which this occurs is called the latent heat of vaporization. As temperature rises, the air can hold more water vapor, and moving air helps replace moist air with drier air, increasing evaporation. Evaporation happens faster in dry air than in wet air, and it occurs more over the ocean than on land. A special type of evaporation is transpiration, which is when plants lose water from their leaves and stems.
- A puddle of water disappears over time because water molecules turn into vapor and escape into the air.
- Vaporization is when a liquid changes into a gas.
- Evaporation is a type of vaporization that happens below the boiling point.
- In a closed container, vapor can’t escape, so the water level stays the same.
- Some water molecules turn into vapor, but an equal number turn back into liquid. This is called condensation.
- For a liquid molecule to become gas, it needs enough energy to break free from other molecules.
- Different molecules have different energy levels; those with enough energy become vapor.
- As evaporation happens, the remaining liquid cools down because it loses energy.
- This is why we feel cooler when sweat evaporates from our skin on a hot day—it absorbs heat from our body and cools us down.
Read More: Polar Vortex
Evaporation links with Humidity
Evaporation raises humidity, especially from the sea and soil, and how quickly it happens depends on the difference in water vapor pressure between the air and the surface. The speed of evaporation is related to how much moisture the air can still hold and how easily air moves through the area. In leaves, how water moves through tiny pores can be more important than airflow.
Condensation Definition
Condensation is the transformation of water vapour into water. If water vapour directly condenses into solid form, it is known as sublimation.
Condensation takes place due to the loss of heat and can occur in one of the following ways:
- Warm moist air rises upwards and expands.
- Warm and moist air comes in contact with the cold surface.
- Warm moist air mixes with the air coming from the colder regions.
Condensation Process
Cloud drops and ice crystals, which are allergic to the Earth’s atmosphere, are linked to suspended aerosols produced by natural and human processes. In the absence of these aerosols, the relative humidity requirements for the spontaneous conversion of water vapour into liquid water or ice crystals would be well above 100% compared to the flat H2O surface.
Forms of Condensation
The transformation of water vapour into liquid is referred to as condensation. Condensation can occur in a variety of ways, including dew, frost, fog, mist, and clouds, depending on the temperature and location. Below are the forms of Condensation:
1. Dew
Dew is formed when moisture collects as water droplets on cooler surfaces. This happens on objects, not in the air. Ideal conditions for dew include clear skies, calm air, high humidity, and cold, long nights. The dew point must be above freezing for dew to form.
2. Frost
Frost is frozen dew. It forms when the temperature drops below freezing. This happens when water droplets on the ground freeze. The conditions for making dew and frost are similar, but frost needs colder temperatures. Frost appears as ice or snow crystals on surfaces.
3. Fog
It is a cloud that forms close to the ground. It happens when warm, humid air cools quickly. Water vapor condenses around dust and smoke in the air. This typically occurs in low temperatures and high humidity, and it can reduce visibility to less than one kilometer. There are 3 types of Fog described below in detail:
| Types of Fog | |
| Radiation Fog | This type of fog is called ground fog. It forms when the ground cools at night, making the air near it cooler too. Long winter nights and clear skies help create this fog. Ground fog can be between 10 and 30 meters thick. |
| Advection Fog | It is formed when there is a fall in the temperature of warm moist air moving horizontally over a cold surface. It is cooled by contact and sometimes by mixing with cold air prevailing over cold surfaces. |
| Frontal or Precipitation Fog | A front is the line where cold and warm air meet. When these air masses come together, fog can form. The warm air rises above the cold air, cools down, and when it reaches the dew point, it creates frontal fog. |
Impatcs of fog:
- Fog makes travel difficult on land, air, and sea because it reduces visibility.
- In cities and industrial areas, smoke and dust help fog form, When fog mixes with smoke, it creates smog, which is harmful to health.
- Fog negatively affects agriculture, especially late-sowing crops.
- Fog is good for tea and coffee plants as it protects them from strong sunlight on hills.
4. Mist
Mist is a type of fog that is less dense. The main difference is that fog reduces visibility to less than 1 km, while mist allows visibility between 1 and 2 km. Mist often forms in mountains when warm air rises and meets a cold surface. Fog is usually drier than mist. Mist can happen naturally, during volcanic activity, or be created artificially.
5. Haze
It is a phenomenon that occurs when dust, smoke, and dry particles reduce visibility. In case of haze, the visibility is reduced from 2 kilometres to 5 kilometres.
Condensation Related Concepts
1. Latent Heat
During evaporation, heat is absorbed and stored in water vapor; this is called latent heat. When water vapor turns back into liquid water through condensation, this heat is released. Latent heat is important for forming storms like typhoons and cyclones.
2. Saturated Air
The air containing moisture to its full capacity at a given temperature is said to be saturated. This means that the air can no longer hold an additional amount of moisture. One hundred per cent humid air is called saturated air.
3. Hygroscopic Nuclei
Condensation always takes place around some particles present in the air. These may be dust particles, smoke, oceanic salts or carbon dioxide which act as nuclei to hold water. They are thus called condensation nuclei or hygroscopic nuclei.
4. Dew Point
The dew point is the temperature at which air becomes saturated with moisture. Smoke and dust particles help water vapor condense. When water vapor condenses, it can form dew, frost, fog, mist, or clouds, depending on the conditions in the air.
Evaporation and Condensation UPSC
We all know that water is made up of molecules that are held together by some force. However, the molecules are free to move independently. Aside from this force, water molecules contain thermal energy generated by extremely fast vibrations. Thus, molecules at the surface move or vibrate with such force that they escape into the air and turn into vapour. This is known as evaporation. Simultaneously, the process is reversible, and molecules can rejoin to form liquids. This is referred to as condensation.
This article will also be useful for other competitive exams such as the UPSC exam. This article discusses evaporation and condensation.
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