✔ 最佳答案
1. Evaporation actually can occur at any temperature in air as far as the relative humidity of air is leass than 100%, i.e. the air is not saturated. The physical process in evaporation is that water molecules with sifficiently high kinetic energy can escape from the water surface into the air, but at the same time, water meolecues from water vapour present in the air can also re-enter into the water. If the air is not saturated (i.e. the air can still have capacity to hold more water molecules), the number of molecules leaving water surface is always greater than the number of water molecules re-entering into the water. Hence, there is a net loss of water molecules from the water. That is to say, the water evapourizes away.
Boiling point is the temperature that most, if not all, water molecules have sufficient energy to go into the air.
2. Following the explanation of the evapouration process given above, it is understandable that in a vacuum, there is no water molecules present in a vacuum that can re-enter into the water. Thus, the net number of molecules ecaping into a vacuum is larger than if air is present. The rate of evaporation of water in vacuum is faster than in air.