According to the kinetic molecular theory of matter, water molecules in an open container are in constant motion due to their kinetic energy. Some of the water molecules at the surface of the liquid have enough kinetic energy to break away from the cohesive forces holding them together and escape into the surrounding environment as vapor. This process is known as evaporation. The rate of evaporation depends on factors such as temperature, surface area, and humidity. So, when water vanishes out of an open container, it is due to the individual water molecules gaining enough energy to escape into the air as vapor.
