What occurs when the rate of molecules transitioning from liquid to gas is equal to the rate of molecules transitioning from gas to liquid?

When the rate of molecules transitioning from liquid to gas equals the rate of molecules transitioning from gas to liquid, a dynamic balance is established. This state is referred to as equilibrium.

In this context, equilibrium specifically pertains to the phase transitions between liquid and gas states. When the rates of the two processes (vaporization and condensation) are equal, the overall amount of liquid and gas remains constant, even though individual molecules are constantly moving between these phases. Consequently, this is characterized as dynamic equilibrium, where both processes are occurring simultaneously at equal rates, leading to a stable condition.

This situation may occur in a closed system at a certain temperature and pressure, where a mixture of liquid and vapor exists. At equilibrium, the properties such as pressure and concentration of each phase do not change despite ongoing molecular transitions, indicating a balance in the system.

While vaporization and condensation are both active processes at equilibrium, they are not described by the other options, which refer to specific conditions or processes rather than the broader concept of equilibrium.