How Does Evaporation Cause Cooling?

“How Does Evaporation Cause Cooling?” this question troubled thinkers and philosophers since ancient times when the concept of evaporation was not even named evaporation. But in modern times we know that Evaporation Cause Cooling because the particles (atoms and molecules) present at the surface of the liquid surface absorb energy from their surroundings and transform it into vapour, which then causes the cooling effect. Evaporation is a type of vaporization that occurs on the surface of liquids and includes the transformation of liquid particles into gaseous particles. As a result, this process is considered to be responsible for the change in the matter state of liquids. Thus, when the heat of evaporation is positive cooling is then caused by the evaporation.

What is Evaporation?

Evaporation is the process of liquid chaning into vapours before achieving its boiling point is called and can only occurs from the surface the liquid.

Evaporation can occur at room temperature which is significantly lower than the boiling point of a liquid as well, it doesn’t require liquid to boil. As liquid molecules have high kinetic energy due to their random motion, they collide with each other and transfer their kinetic energy from this collision. Some of these molecules which become highly energized, turn into gas and escape from the liquid.

Know more about Evaporation

How Does Evaporation Cause Cooling?

Natural cooling is caused by evaporation. The basic concept is that in order for matter to change state, it must either receive or lose energy. When matter molecules shift phases from liquid to gas, they require energy to overcome their potential energy through kinetic energy. As a result, the liquid absorbs energy from its surroundings. 

When energy is transmitted, the temperature of the material rises or falls depending on whether the energy is transferred from the substance to the surroundings or vice versa. There are, however, exceptions to this rule. Although the temperature of the material rises until the boiling point is reached during evaporation, there is no visible heat transfer.

The molecules of the material constantly absorb heat energy from their environment and also from the collision of other molecules until these molecules have enough energy, at which point they begin to break away from the liquid and transform into vapour. Because there is no temperature difference until the evaporation process has been completed, i.e. the complete liquid is changed into vapour, the energy required for this phase change is referred to as the latent heat of vaporization, implying that this heat will not affect the temperature interpreting on a thermometer.

Applications of Evaporative Cooling

There are several applications of Evaporative cooling in daily life, some of which are as follows:

Chilly Sensation on Touch of Spirits

When we put some spirit or petrol on the back of our hands and wave them about, the spirit soon evaporates and our hands get extremely chilly. This is due to the fact that the spirit requires latent vaporization heat to transition from a liquid to a vaporized form. The spirit pulls this dormant vaporizing energy from our grasp. The hand loses heat and cools down.

Working of Earthen Pot

During hot summer days, water is frequently kept cold in a clay pot called a pitcher or a Matka. For cooling during hot summer days, water is generally kept in an earthen pot known as a pitcher or Matka. The earthen pot contains a huge number of extremely small pores, or holes, in its walls. Some of the water is constantly passing through these pores to the pot outside. This water evaporates constantly, absorbing the latent heat necessary for vaporization from the clay pot and the remaining water. As a result, the remaining water loses heat and becomes chilly. This is an example of evaporation-induced cooling as well. It should be mentioned that owing to the large value of the latent heat of water vaporization, all of the water on the planet does not evaporate.

Cooling of Homes

During the hot summer evenings, many people, especially in villages, sprinkle water on the ground in front of their homes. This water evaporates by eliminating the high latent heat of vaporization from the ground and surrounding air. After the heat is removed from the area, it becomes chilly and comfortable. The water that evaporates from the leaves of trees cools the surrounding air in the same manner.

Cooling of Body

Perspiration, often known as sweating, is the mechanism through which our bodies maintain a constant temperature. When our body temperature rises too high on a hot day or after engaging in strenuous exercise, our sweat glands release moisture or perspiration on our bodies. When perspiration evaporates, our bodies absorb the vaporizing latent heat. This keeps our bodies cool.

Desert Cooler

A desert cooler cools better on a hot and dry day since it operates on the evaporation principle. The greater the temperature on a hot day, the slower the rate of water evaporation Thus, the higher the rate of water evaporation. As a result of the higher rate of water evaporation, a desert cooler cools better on a hot and dry day.

Temperature of Tea

It’s a well-known fact that humans can drink hot tea from a saucer faster than from a cup. Surface area is one of the factors affecting the rate of evaporation and the saucer has a large surface area. Because of the huge surface area of the saucer, hot tea evaporates more quickly. This rapid evaporation cools the hot tea faster in a saucer than in a cup, making it easier to drink from a saucer.

What is Condensation?

Condensation is the opposite process of evaporation. In evaporation heating water make to change its phase from liquid to gas, but in the case of condensation water vapours (gaseous form) come in contact with a cold object to form water droplets. Thus, condensation is defined as the process in which water vapours cool in the presence of any cooler substance to form water droplets.

We readily see condensation in our daily life such as the water droplets collected on the plate that is placed on the boiling water is an example of condensation.

Sample Questions on Evaporation Cause Cooling

Question 1: Why does everybody wear cotton clothes in summer? 

Solution:

During summer, we perspire (sweat) a lot due to our body’s mechanism of cooling by evaporation of sweat which takes heat from the body and makes the body cool. Cotton, being a good absorber of sweat, absorbs the sweat and helps in increasing the speed of the evaporation by increasing the surface area and exposing it to the atmosphere.

Question 2: How does water keep in the earthen pot (matka) remains cool?

Solution:

When we kept water on the earthen pot (matka), the water molecules evaporate from the several tiny pores of the pot. During this process, it takes the heat from the water and thus the water cools down due to the loss of heat. This is the reason why water kept in earthen pot keep cool.

Question 3: We often sprinkle water on the ground or on the roofs during summer. Why?

Solution:

This is because when we sprinkle water over the ground or roof top, the water from there evaporates taking the heat from the ground or roof top and in the process making it cool.  

Question 4: We are able to sip hot tea or milk on a saucer rather than a cup. Give reasons.

Solution:

We know that the rate of evaporation increases as the surface area of the liquid increases. Thus, when we put the hot milk or tea on a saucer, the surface of the liquid increases, thus the rate of evaporation of the milk or tea increases and due to increase in the rate of evaporation, more heat is taken from the hot milk or tea and it cools down more rapidly as compared to when it was in the cup and we are easily able to sip the hot milk or tea on saucer rather than a cup.

Question 5: Why does our palm feel cold when we put some acetone or perfume on it?

Answer:

When we pour some acetone or petrol on our palm, the acetone or perfume starts evaporating. In this process, it takes the necessary heat required from our palm and due to loss of heat we feel cold. This is the reason why our palm feels cold when we put some acetone or perfume on it.

Question 6: How do air coolers work on the principle of Evaporation? 

Answer:

This is because of the working mechanism of the air cooler. The air coolers has an exhaust fan which sucks in the dry air of the room inside. In the cooler there is a pad that has been wet by water. The water evaporates from the pad by taking the heat from the dry air thus, in the process making the air cool. This cool air released from the air coolers which circulates inside the room. Thus, air coolers work on the principle of cooling effect caused by Evaporation.

Question 7: We feel cool when we apply hand sanitizers to our hands. Give a reason Why?

Answer:

The sanitizers that we apply over our hand contains alcohol as one of it’s primary constituent and the alcohol evaporates much faster than water. Thus, when we apply hand sanitizers over our hand, the alcohol starts evaporating by taking the heat from our own body and thus, due to the loss of heat from our body, we feel cool.

Question 8: In summer our clothes dry up much quicker compared to winter and monsoons. Why?

Answer:

During summer, the temperature is higher than winter and monsoons and we know that the rate of evaporation is directly dependent on the temperature, so in summer clothes dry up much faster in summer in comparison to winter and monsoon. Another important factor is humidity, in summer humidity in air is much less than that in monsoon, thus clothes dry up slowly in monsoons.  

FAQs on How Does Evaporation Cause Cooling?

Q1: What is Evaporation?

Answer:

Evaporation is defined as the process in which a liquid changes its form from the liquid phase to the gaseous phase below the boiling point of the liquid.

Q2: What are Factors Affecting Evaporation?

Answer:

There are several factors affecting the process of evaporation such as temperature, the surface area of liquid, the humidity of environment, and wind speed in the surrounding.

Q3: What is Rate of Evaporation?

Answer:

The rate of Evaporation is the ratio of time required to evaporate a test solvent to the time required to evaporate the reference solvent.

Q4: Why does Evaporation Require Energy?

Answer:

Evaporation requires energy because it occurs when intermolecular bonds between liquid molecules break, and to break those bonds some amount of energy is required. This required energy is provided by the surrounding environment, hence it causes a cooling effect.

Q5: What are Examples of Everyday processes that use Evaporation to Cause Cooling?

Answer:

There are various examples of evaporation in our daily life, some of which include the cooling effect after sweat, working of water coolers, working of earthen pots, drying of wet clothes, etc.

Q6: What are the Liquids that have the Highest Rate of Evaporation?

Answer:

Acetone, Petrol, and Alcohols are some examples of liquids that have a high rate of evaporation. We can observe this as by putting these substances on the skin we experience a cold feel directly at the spot of application.