A small container is filled with liquid water. What can happen if the container of water is an open system that couldn’t happen if it were a closed or isolated system?

Answer 1

Liquid water is always evaporating because statistically there are always molecules near the liquid-vapor surface which have enough energy to escape as gas molecules to become water vapor. If the water container is closed, then this evaporation process will continue, but at the same time water vapor will condense back into the liquid. Eventually, equilibrium will be achieved where the rate of evaporation is equal to the rate of condensation. However, if there is no lid, then the water vapor molecules will escape and there will never be an equal rate of condensation to equal the rate of evaporation, and you will notice that the liquid water will begin to slowly disappear.

Answer 2

One obvious thing that could happen in an open system that wouldn't happen in a closed system is that the liquid water could evaporate, i.e. turn into a vapor/gas.