Chapter 12, Problem 12.64QE

Interpretation Introduction

Interpretation:

The vapor pressure (in torr) of cyclohexane above the solution has to be calculated.

Concept Introduction:

Vapor pressure depression:  The equilibrium between a liquid and its vapor produces a characteristic vapor pressure for each substance that depends on the temperature.  The lowering of the vapor pressure is caused by a lesser ability of the solvent to evaporate, so equilibrium is reached with a smaller concentration of the solvent in the gas phase.  The vapor pressure of a solution is expressed using Raoult’s law:

  

The vapor pressure of the solvent above a dilute solution is equal to the mole fraction of the solvent times the vapor pressure of the pure solvent   The difference between the vapor pressure of the pure solvent and the vapor pressure of the solution is proportional to the concentration of the solute and is given by the equation,

  

The vapor pressure depression of the solvent is a colligative property, because it is proportional to the concentration of the solute.  Raoult’s law is applicable to dilute solution.