Difficult Pressure Q

[SonhosDaVida]

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Can someone explain to me why the vapor pressure of methanol increases if put into a new beaker? For Q6.



 

[SonhosDaVida]

I understand why the moles of methanol increase. It is due to fractional distillation, which after each evaporation condensation cycle, makes the lower BP substance vapor pressure greater, making the higher BP substsnce more pure in solution.

But why does the total vapor pressure increase!?!? I thought that VP of methanol increases and VP of ethanol decreases, so shouldn't the overall VP stay the same in fractional distillation?

 

[Flufpot12]

I think the total vapor increases because there is mostly methanol in the new beaker and it’s evaporating more easily because there are fewer ethanol molecules blocking its path. The vapor pressure of ethanol decreases because there’s a lower chance of it evaporating now, but the decrease is relatively smaller (compared to the increase in methanol’s vapor pressure) since it wasn’t evaporating much before either