Chemistry 122: vapor pressure

Chemistry 122: vapor pressure - Chemistry 122 Liquids boil...

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Chemistry 122 1/29/2014 Liquids boil when the vapor pressure (VP) equals to the air pressure of the surroundings, so a lower VP means a higher boiling point Due to solute- solvent intermolecular attraction, higher concentrations of nonvolatile solutes make it harder for solvent to escape the vapor phase. Therefore, the vapor pressure of a solution is lower than that of the pure solvent. The vapor pressure of a volatile solvent above a solution containing a non-volatile solute is proportional to the solvent’s concentration in solution: Raoult’s Law P solution = X solvent P solvent X A is the mole fraction of the solvent and P A is the vapor pressure of the pure solvent. Note: This is one of those times when you want to make sure you have the vapor pressure of the solvent . Xsolvent= # of moles solvent/ (moles solution) Moles solution  moles of solute +moles of solvent Example : vapor P of pure H 2 O at 20º C is P H2O = 17.5 torr. If we keep the temperature
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