Video Transcript
In a closed system, a constant
vapor pressure results from the formation of a dynamic equilibrium between the vapor
and the liquid. At this equilibrium, which two
opposing processes are occurring at the same rate?
The vapor pressure is the pressure
exerted by a vapor above its liquid when the vapor and the liquid are in equilibrium
with each other. The equilibrium that is reached
inside this beaker is a dynamic equilibrium. In a dynamic equilibrium, two
processes are occurring at the same rate, so no macroscopic change is observed. If we could look inside our beaker
at the atomic level, we’d see that the molecules inside are constantly moving. In fact, sometimes we would see
molecules in the liquid phase gain enough energy to become a vapor, which describes
the process of evaporation. At the same time, we would also see
the molecules in the vapor phase join the liquid phase if they lose enough
energy. In other words, those molecules are
condensing.
Because the processes of
evaporation and condensation are occurring at the same rate, there is a dynamic
equilibrium between the vapor and the liquid, which results in a constant vapor
pressure. So the two opposing processes that
are occurring at the same rate are the evaporation of the liquid and the
condensation of the vapor.
