Properties of Volatile Nonelectrolyte Solutions

What is the effect on vapor pressure when the solute is volatile, that is, when the vapor consists of solute and solvent molecules From Raoult s law (Equation 13.9), we know that 

Ftolal Fsolvenl b (- solvent F Qivent) i (- solute solute) 

Just as a nonvolatile solute lowers the vapor pressure of the solvent by making the mole fraction of the solvent less than 1, the presence of each volatile component lowers the vapor pressure of the other by making each mole fraction less than 1. 

Let s examine this effect in a solution that contains equal amounts (mol) of benzene (CgHg) and toluene (CyHg) = Atoi = 0.500. At 25°C, the vapor 

As you can see, the presence of benzene lowers the vapor pressure of toluene, and vice versa. 

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