Vapor pressure concept

[DeeVeeZee]

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Hey guys,

I am struggling with a concept, please let me know if I am way off on this one. So when two liquids of different standard vapor pressures are mixed, I believe that this vapor pressure above the solution is a range between the lowest volatile and highest volatile substance if mor than one present right? Does this follow the equation Ptotal=Pa+Pb...

My intuition is lacking here because these seem to conflict for me. The equation says that the pressures should add while my brain says its a range. Am I confusing something here. Any help is greatly appreciated.

Thanks

 

[onedirection]

Hey guys,

I am struggling with a concept, please let me know if I am way off on this one. So when two liquids of different standard vapor pressures are mixed, I believe that this vapor pressure above the solution is a range between the lowest volatile and highest volatile substance if mor than one present right? Does this follow the equation Ptotal=Pa+Pb...

My intuition is lacking here because these seem to conflict for me. The equation says that the pressures should add while my brain says its a range. Am I confusing something here. Any help is greatly appreciated.

Thanks

It kind of does fall in a range

Because

Ptot = XaPa + XbPb

you have to take into account mole fraction

 

[monkeyvokes]

yes, you have to multiple their pressures by the mole fraction as one direction stated.
Also, if the solution is not ideal then you have to take into consideration the breaking and forming of bonds. If the mixing of solvents is exothermic, then the pressure is lower than expected (its giving off energy so must be forming better bonds that are less likely to break and evaporate). If endothermic, the pressure is higher.