Factors affecting rate of evaporation are temperature, surface area, speed of wind etc. Evaporation as the name suggests is a type of vaporization. It is defined as a process or phenomenon where the state of matter changes from liquid to gaseous state below at the boiling point. In the context of a water cycle, the liquid water changes into gaseous water vapors in the atmosphere.
Another method where there is a conversion of water to vapor is called boiling. The difference between boiling and evaporation is by the temperature supplied to the liquid phase. Boiling happens at 212F and evaporation starts at 32F. This is the reason why evaporation is a slow and natural process of phase transition where conditions and amounts of liquid are of great significance.
Figure 1: Principle of Evaporation
The rate of evaporation exhibits the speed at which the evaporation is happening in daily life or the atmosphere. There are certain scenarios or circumstances which affect the way evaporation takes place. These factors are listed below −
Temperature exposure
Surface area
Moisture and humidity in the atmosphere
Speed of wind
Viscosity and intermolecular attraction among the molecules
Atmospheric pressure
Depth of the liquid body
The difference in the vapor pressure to the atmosphere.
Presence of foreign particles in the liquid
Magnetic field influence
The rate of evaporation is directly proportional to the temperature after exposure to. This means that the temperature of a liquid will be its rate of evaporation.
An increase in temperature increases the kinetic energy of the atoms which in turn decreases the intermolecular attraction and increases the intermolecular space. This leads to phase transition from liquid to the gaseous phase hence, an increase in the rate of evaporation.
Example: Drying clothes in the summer season.
Like temperature, the surface area of liquid is also directly dependent on the rate of evaporation. Liquid as a state of matter has many properties associated with it but the one which is useful here is its ability to take any form and shape.
Likewise, if a liquid is put in a container with more surface area then some of its particles get easily exposed which increases the rate of evaporation.
Example: Spreading clothes provide more surface area and easy drying.
Moisture and humidity in the atmosphere are the water vapors which already present in the atmosphere. When the air is humid then it becomes very difficult for the air to aid in the process of evaporation.
The rate of evaporation slows down due to the inability to the conversion of water into water vapor. Hence, more is the more moisture in the environment or the climate less will be the rate of evaporation.
Example: On a humid day because of more water vapors the drying of clothes is not quick
The speedy wind is the best aid for evaporation. A fast blowing wind helps in increasing the kinetic energy of the water particles and it also disperses the hanged water vapour in the environment thereby providing room for evaporation.
Example: Windy days are best when it comes to drying clothes as compared to humid days.
Viscosity is the property of a molecule which indicates its fluidity. So according to that viscosity and intermolecular attractions are related to one another. If a liquid has high viscosity then it implies that the intermolecular forces are strong which in turn decreases the rate of evaporation and vice versa.
Example: Honey is more viscous than water. So its molecules are more tightly bound than water. Hence it will not be easy for honey to evaporate.
Many pieces of research have shown that atmospheric pressure has a great influence on the rate of evaporation. The places on the earth where atmospheric pressure is less have shown a high rate of evaporation.
Pressure is inversely proportional to temperature. So, high atmospheric pressure brings the molecules closer to each other by reducing spaces and increasing attraction thereby preventing phase transition from liquid to gas.
Example: Storms are in a high-pressure state which prevents escaping of water into the water vapors.
Water or liquid evaporation is guided by many factors but there are certain drivers which maintain that evaporation rate. For maintaining and sustaining the rate of evaporation energy is required. This huge amount of energy is called Latent heat of vaporization.
When water evaporation takes place the energy required for it is solar radiation and many other radiative emissions. When these radiations hit the surface of liquid these are penetrated to a certain depth according to the liquid composition.
This stores the heat and decreases the temperature thereby; affecting the rate of evaporation. Hence, more is the depth of the liquid body; the less will be the rate of evaporation.
Example: A shallow pond easily evaporated as compared to a river due to the huge difference in depth.
Differences in the vapor pressure of the atmosphere and the rate at which the air leaves the surface is a basic factor influencing the rate of evaporation.
The rate of evaporation always depends on this factor as it can be a positive or negative outcome according to the difference.
Impurities whether soluble or insoluble in water do affect the rate of evaporation. Soluble impurities are dissolved in water under dynamic equilibrium conditions where these impure particles occupy the space between the water molecules. These soluble impurities have higher boiling points than water. Due to this, the concentration of soluble impurity is more in the water which increases the rate of evaporation.
On the other hand, insoluble impurities do not have much influence on the rate of evaporation because these settle down at the bottom as sediments and do not change the composition of the liquid.
Example: Separation of salt from water is through evaporation procedures.
In recent times, it has been confirmed by many studies that, like other traditional parameters, magnetic fields have a significant effect on the rate of evaporation. When a polarizing external field is applied to liquids, especially water then there is a change in the bonding patterns existing in it.
The application of a static magnetic field under different conditions affects the evaporation rate. Usually, it increases the viscosity which in turn weakens the intermolecular forces thereby, results in easy evaporation. A statistical study has shown that magnetic influence can increase the rate of evaporation in water even in low-temperature environments.
In various industrial procedures like, printing, coating, separation of molecules, and drying of a variety of materials of cloth and chemicals, wood evaporation takes place or is used as a technique.
In various academic laboratories, evaporation process is used for drying samples as in chromatography and spectroscopy. Various instrumentation techniques are used like centrifugal evaporator or rotary evaporator.
In daily life chores like drying clothes, cooling hot dishes, or application of nail polish rate of evaporation happens naturally
Evaporation is also observed in various biogeochemical cycles for proper ecological balance. E.g. Water cycle.
In this topic of evaporation is a very important but simple phenomenon happening in nature and used by mankind as well to carry on daily activities and big procedures. It is one of the procedures which maintain the desired dynamic equilibrium and balance between the states of matter which is essential for the smooth functioning of life on earth.
Q1. What is the difference between evaporation and boiling?
Ans. Evaporation is a natural process that is observed in changed conditions. Boiling is an unnatural or induced process where the desired level of temperature and pressure is provided with continuous heating of the liquid. Evaporation is a surface phenomenon with no bubbling effect. Boiling is the complete opposite as it is a bulk phenomenon with significant bubbling. The last easily observable difference between evaporation and boiling is time. Evaporation is a slow process and boiling is a fast process.
Q2. How is evaporation observed in the dairy industry?
Ans. Evaporation as a technique frequently observed in the dairy industry. It is used for drying the milk in the form of milk powder which is a separation technique carried out to evaporation of water content. In condensing milk again evaporation is used which thickens the milk and fat content removing the water.
Q3. Name the type of compounds which show easy evaporation with an aroma.
Ans. Covalent compounds can easily evaporate with a pungent smell. This is because as compared to other bonding types it is very weak and can easily break.
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