Evaporation and Boiling: Kinetic vs Potential energy

Evaporation and boiling are two related but different processes that involve the conversion of a liquid to its gaseous form. Both processes involve the molecules of a liquid gaining enough energy to overcome the intermolecular forces that hold them together in the liquid phase.

One important difference between evaporation and boiling is evaporation can occur at any temperature, as long as there is enough kinetic energy for molecules to escape from the liquid surface. Boiling, on the other hand, occurs at the saturation temperature of the liquid, where the vapor pressure of the liquid is equal to the atmospheric pressure.

Boiling involves the conversion of potential energy (from heat) into kinetic energy (increased molecular movement), while evaporation is solely driven by the kinetic energy of the molecules in the liquid.

Who provides energy for evaporation?

The surroundings provide energy for evaporation.

How?

Molecules are always in motion with different amounts of kinetic energy. Refer to Maxwell - Boltzmann distribution of kinetic energy.

It says the following:

Maxwell -Boltzmann. energy distribution shows that while the average kinetic energy (or speed) of molecules in a gas remains constant at a given temperature, individual molecules within the gas can have different speeds. This variation in speeds is due to the random nature of molecular collisions and the transfer of momentum during these collisions. The distribution describes the probability of finding a molecule in the gas with a particular speed, with the majority of molecules having speeds around the average value.

Detail

Evaporation occurs at the surface of a liquid and is driven by the kinetic energy of some of the molecules in the liquid. These molecules gain enough energy to break free from the liquid and enter the gas phase. As these molecules leave the liquid, they take away energy in the form of heat, causing the remaining liquid to cool. Evaporation can occur at any temperature below the boiling point of a liquid.

Boiling, on the other hand, occurs throughout the bulk of the liquid and requires the supply of external heat. When a liquid reaches its saturation temperature, it is said to be saturated with energy. Additional heat supplied to the liquid causes the molecules to gain even more energy, breaking the intermolecular bonds and causing the liquid to expand rapidly into a vapor.

This turbulence in the liquid is what we refer to as boiling.

In summary, evaporation is a surface phenomenon driven by the kinetic energy of molecules, while boiling is a bulk phenomenon that requires the supply of external heat. Both processes involve the conversion of a liquid to a gas, but they differ in the way they occur and the conditions under which they take place.