Little bit confused on what each of these concepts are. So far i understand that the ideal gas law tells us how much pressure an amount of gas exerts on the walls of a container. I also understand that the saturated vapor pressure is the pressure applied on the container from a substance in liquid/vapor equilibrium. What i dont get is whether these two concepts are related. Like are the pressures the same? If I use the ideal gas law equation to calculate the pressure would that be the same as the pressure of the saturated vapor pressure?
[Physics] Difference between ideal gas law and saturated vapor pressure
ideal-gaspressure
Best Answer
The ideal gas law strictly applies only to ideal gases, which do not condense to form a liquid. This means that there is no vapor pressure associated with ideal gases, which are used to represent real gases that are at a temperature that is very much higher than their condensation temperature.
Regarding vapor pressure, practically every liquid contains atoms or molecules that have enough velocity to escape into the vapor phase. In a closed and evacuated container that initially contains only a liquid such as water, these molecules will move into the vapor phase at a rate that depends on the temperature of the liquid. With no outside heat source, such a liquid will lose temperature as this happens, so heat input to this system is required to hold the liquid temperature at a specified value as water evaporates.
As more and more molecules enter the vapor space, there will be water molecules that strike the liquid surface and re-condense. Thus, there is a rate at which water in the container evaporates and a rate at which water in the container condenses. Assuming a constant temperature, and a constant rate of water evaporation, the water vapor density rises with time, as does the rate of water vapor molecules striking the water surface and re-condensing. At equilibrium, the rate of water evaporation and water condensation are equal.
Water vapor molecules in the vapor space of the container are also striking the surfaces of the container, producing pressure as a result. At the equilibrium point, the pressure that is produced is the vapor pressure of the liquid. This vapor pressure is related to the liquid temperature via the Antoine equation. For much more information, see https://en.wikipedia.org/wiki/Antoine_equation