Vapor Pressure

Vapor Pressure and Enthalpy of Vaporization, Clausius-Clapeyron equation

Clausius-Clapeyron equation is stated below:

where P1 and P2 are any two vapor pressure measured at T1 and T2 respectively,delta Hvap is the enthalpy of vaporization, the negative sign represents its endothermic nature,R is the gas constant(R=8.3144621 j/mol*K).
Vapor pressure is best described by an example of water in a closed container. As every liquid tends to evaporate into gaseous phase,evaporated gas,once hit the ceiling of the container,condenses back into the liquid state. So, there will be an equilibrium reached once the rate at which the molecules escape liquid phase equals the rate of molecules falling back into the liquid phase. Vapor pressure is measured when the equilibrium is reached. So vapor pressure is the equilibrium vapor pressure, basically. What we call a volatile substance must have high vapor pressure. Another aspect that is associated with vapor pressure is the boiling point. High boiling point~ low vapor pressure; low boiling point~ high vapor pressure. But this relation is different from that of Temperature and Eq.Vapor pressure. Because, higher the temperature, higher the kinetic energy of the molecules,consequently, more volatile the molecules in liquid phase will become.

I forgot to mention about the boiling point and intermolecular force relation.As the intermolecular forces between the molecules are strong enough to hold them intact, it means, it will take lot of energy to break those forces and bring the liquid to evaporate(boil). So stronger the IMF, higher the BP( boiling point).

Condensation is the reverse process of vaporization. Molecules in gas phase transfers some of its kinetic energy by colliding with slower gaseous molecules and solid objects( walls of the container). If this molecule loses sufficient energy and comes in contact with the surface of the liquid, it can re-enter the liquid phase.