Evaporation and boiling: are they the same thing when only one substance is involved?

Another way to put it: Is evaporation possible when only one substance is involved?

Consider a closed vessel with water in gas and liquid state, in equilibrium. At the interface, the same amount of molecules migrate from liquid to gas and the inverse (dynamic equilibrium). Now, if we remove X molecules from the gas phase, molecules from the liquid phase will pass to the gas phase until equilibrium is achieved again.

What is the process describing this phase transition of the liquid molecules to gas: evaporation or boiling?

These are two types of vaporization. The definition from wikipedia (en.wikipedia.org/wiki/Vaporization) are rephrased below in order to mark their difference.

• Evaporation (surface) occurs when the equilibrium vapor pressure is higher than the partial pressure of vapor of the substance.

• Boiling (volume) occurs when the equilibrium vapor pressure is higher than the pressure of the "environmental pressure" (which I intepret as the total pressure surrounding gas).

I understand that in a single substance, the two cases are the same. Is this correct?

In other words, how would it be possible to achieve only evaporation in the single substance case. If by removing the X gas molecules will result in a pressure decrease. This suits best at the boiling definition.

• In my opinion, the difference between evaporation and boiling is only a matter of degree. In other words, boiling is just very fast evaporation. Dec 12, 2020 at 17:38
• I don't think that it is a quantitative issue. If we consider a system of atmospheric air and water - there is a qualitative difference between evaporation and boiling. Namely, evaporation takes place under specific conditions (not saturated air, any temperature) and boiling under different specific conditions (boiling temperature). My problem is that I cannot see this distinction in a single-substance system. To my understanding, in a single-substance system, both evaporation and boiling occurs under the same conditions.
– Jore
Dec 12, 2020 at 23:31
• When the vapor pressure of liquid water becomes slightly higher than the partial pressure of water vapor above that water, it boils, whether there is air and water vapor above the liquid water or only water vapor above the liquid water. For "evaporation", the rate of boiling is very low, it is constrained by how fast the liquid water can absorb heat from the environment, and it occurs at the liquid water surface. "Boiling" occurs on the bottom of a container at the heat source, and it is a very fast process due to the high rate of heat transfer. The processes are equivalent. Dec 13, 2020 at 0:25