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Vapor Pressure and Boiling Point
- Vapor pressure is the pressure exerted by the vapor particles (in the gas phase) above a liquid layer (the system must be closed, in other word, the container is sealed).
- Vapor pressure is directly related to the intermolecular force (IMF) keeping the liquid molecules held together. Therefore, the higher the IMF, the less amount of vapor particles are in the gas phase, and therefore, the lower the vapor pressure.
- Boiling point is the temperature where the vapor pressure = atmospheric pressure.
Boiling point is a function of IMF and MW, molecular weight or molar mass.
- In this lab, we will look at the intermolecular forces in the substance to predict which substance has the highest vapor pressure (thereby determining which has the greater boiling point).