Main Difference – Evaporation vs Boiling
Both evaporation and boiling are methods of vaporization found in liquids. They differ from each other due to the speed and the state of vaporization. Evaporation is the vaporization of a liquid at room temperature whereas boiling refers to the vaporization of a liquid when heated to its boiling point. This is the main difference between evaporation and boiling.
What is Evaporation
This is a spontaneous process that occurs at room temperature due to the movement of high energy liquid molecules escaping into the air. Molecules in a liquid have a certain degree of freedom of movement and possess different amounts of kinetic energy. Therefore, the molecules with a higher amount of kinetic energy have the tendency of escaping into the gaseous phase overcoming the stresses that might hold them back. Usually, the molecules that get evaporated are the ones at the surface of the liquid as they require a small amount of energy to escape from the liquid phase. However, a less percentage of molecules deeper in the liquid can get evaporated provided that they have an adequate amount of kinetic energy to get past the surface of the liquid avoiding collisions within the liquid.
Evaporation takes place as long as the air above the liquid remains unsaturated. This means that the air above the liquid should be capable of accommodating the incoming liquid vapor molecules. These molecules absorb the heat energy from the liquid which is converted into their kinetic energy. Therefore, upon the evaporation of the liquid molecules, the temperature of the rest of the liquid body decreases.
What is Boiling
As mentioned above, boiling is the process of vaporization of a liquid when heated to its boiling point. The temperature where a liquid begins to turn into its vapor form is called the liquid’s boiling point, and it is a property of the liquid. When heated, the molecules within the liquid are able to absorb the heat energy provided and increase its kinetic energy. As a result, the rate of evaporation increases. This takes place as long as the air remains unsaturated. However, at the point when the internal pressure of the liquid becomes equal to the external pressure (ambient pressure), the conversion of the liquid molecules into vapor is called ‘boiling.’
This process takes place at a constant temperature, and the temperature remains constant until the entire liquid body is changed into its vapor form. Unlike in the case of evaporation, the entire liquid body takes part in the boiling process.
Difference Between Evaporation and Boiling
Definition
Evaporation is the process of vaporization of a liquid at room temperature.
Boiling is the process of evaporation of a liquid at the boiling point of the liquid.
Temperature Contribution
Evaporation takes place at any given temperature.
Boiling takes place only at the boiling point of the liquid, and this temperature remains constant from the beginning till the end of the boiling process
Behavior of Liquid Molecules
Evaporation takes place mainly at the surface of the liquid. Therefore, the surface molecules take part in this process most of the time.
Boiling takes place throughout the entire liquid.
Effect on bulk liquid body
When evaporation takes place, the temperature of the liquid body decreases.
The temperature remains constant throughout the boiling process.
Quality of the air above the liquid phase
Evaporation takes place as long as the air above the liquid remains unsaturated.
Boiling takes place when the internal liquid pressure is equal to the external pressure (ambient pressure).
Image Courtesy:
“Vaporization” by Tristan Schmurr –(CC BY 2.0) via Flickr
“Boiling Water” by Scott Akerman (CC BY 2.0) via Flickr
