I know it is confusing concept, but think this way: when you have higher vapor pressure, you already have vapor, you need less heat to boil(lower boiling point). I tried to simplize it. (boiling point) ~ 1/(vapor pressure)
but what is vapor pressure?
vapor pressure : the pressure exsist in equilibrum between molecule in liqiud satge with its vapor. in other hand when you have one glass water, in you glass water you have H20 liquid and H2O Vapor(gas).{ that is the reason why if you leave one glass water in room temprature after a while all your water vaporize without reciving to 100 degree}
Note: this pressure exsist inside the liquid.(inside your glass water).
Now you can manuplate the concept. when vapor pressure is high for example "Acetone" , you have more Acetone molecule in "Gas" form inside your acetone liquid then with a little bit affort(heat or energy) this gas molecule will scape, what is the meaning of that?
means you have lower boiling point:
important note 1: always keep in mind hydrogyn bond decrease your vapor pressure then increase your boiling point.
important note 2: after you check for hydrogyn bond, you go for molar mass, if we don't have hydrogyn bond, check for weight, higher molar mass( heavier) low vapor pressure and higher boiling point.
know lets make a multipy choise question:
which one has lower boilng point:
A) Water ( molar mass 18)
B) Ethanol( regular alchol) ( molar mass 46)
C) Acetic acid ( molar mass 60)
D) Acetone ( molar mass 58)
E)Normal Hexane (molar mass 86)
and you know the answer gonna be D, because A, B, C have hydrogyn bond( lower vapor pressure, higher boiling point)
between Hexane( C6H12) and Acetone (C3H6O) which don't have Hydrogyn bond, Acetone is lighter, then has higher vapor pressure and result lower boiling point.
hopefully it help.
