Boiling and Evaporation: A Comparative Analysis

Boiling and Evaporation are both physical changes or phase changes where the liquid transitions into the gaseous state. But there are key differences.

Evaporation of a liquid can take place at all ranges of temperature. Think of clothes hanging on a clothesline to dry or the ink from your fountain pen drying up on paper. Evaporation takes time and is a gradual process. Keep a small amount of water in a container in the hot sun. You will see the water level gradually decrease. Eventually, all of the water evaporates. Evaporation happens at the surface of a liquid. Liquid evaporates faster from a wide mouthed vessel where more of the liquid surface is exposed to the air.

Boiling, on the other hand, requires a specific temperature, the boiling point. At this temperature boiling happens throughout the liquid. All of the liquid transitions into gaseous state and during this change the temperature remains the same. When you place a kettle of water on the stove, you can see bubbles form throughout the liquid. Boiling takes place faster because all of the liquid particles gain enough energy.

Liquid particles are constantly in motion. Some particles have more than the others but the average energy of the all the particles remain constant.

Particles of the liquid that are higher in energy on the surface can escape as a gas. They can escape because they are only held by the particles of liquid beneath them. The other layers of liquid particles have particles of liquid that attract them from all directions. Hence it is not possible for the particles of a liquid to evaporate from layers beneath the surface. Hence evaporation is a surface phenomenon.

When a liquid boils, all of the particles gain energy. All the layers of particles can escape as a gas. This happens regardless of whether they are on the surface or deep within the liquid. Hence Boiling happens throughout the liquid but at a specific temperature, the boiling point, the temperature at which all the liquid particles gain enough energy to overcome the inter particular forces of attraction

Dear students, it would be interesting to read everyday examples of boiling and evaporation. If you have an example in mind, do type in your comments.