When a liquid is sealed in a closed container at a constant temperature, the vapor pressure reaches a point of equilibrium over time. At this point, the number of molecules escaping the liquid’s surface into the vapor phase equals the number of molecules condensing back into the liquid. So, while it might seem that nothing is happening because the container is closed and the temperature is constant, vapor pressure will increase initially until it stabilizes at the liquid’s equilibrium vapor pressure.
In a closed system, the liquid molecules can only escape into the vapor space above them and can’t be lost to the external environment. This leads to a gradual increase in vapor pressure until it reflects the specific properties of the liquid at that temperature. However, once equilibrium is reached, the vapor pressure will remain constant as long as the temperature stays the same and no additional factors are introduced.