Vapor pressure confusion

[Tokspor]

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I am confused about whether vapor pressure is a fixed property or if it is just something which increases with temperature. Consider this: a decrease in vapor pressure corresponds to an increase in the boiling point. What this means is that the phase diagram will shift to the right. So now, at any given pressure, it takes a higher temperature to get to that point where liquid turns to gas. So how do you get to that boiling point? You increase the temperature. But when you increase the temperature, vapor pressure is supposed to increase as well. But when vapor pressure increases, the boiling point decreases, so now we're at a different phase equilibrium again. What property is supposed to be fixed here? Everything seems to be moving around.

 

[premed101]

I think your misunderstanding lies within why the boiling point rises with decreasing vapor pressure.
Boiling occurs only when vapor pressure from the liquid equals atmospheric pressure. If you increase the vapor pressure of your liquid, you will hit atm pressure faster and less temperature will be needed than as if you haven't increased the vapor pressure.
When vapor pressure increases due to increasing temperature, it is getting toward its boiling point.
The reason a decrease in Vapor pressure results in an apparent increase in boiling point is because you will now have to add more heat than if the vapor pressure were higher.
I admit, it's complicated! Do you understand now?

 

[Doodl3s]

So, every liquid has its own unique vapor pressures that are proportional to the temperature of the liquid...
So, at 50 degrees, lets say water has a vapor pressure of .5 atm... it is 1 atm at a 100 degrees and boils

HOWEVER, there are other liquids that have a vapor pressure of .2 atm at 50 degrees. So having a lower intrinsic vapor pressure means it will have a higher boiling.

so when they say something has a lower vapor pressure when they're comparing the two substances, they're probably assuming both substances are at the same temperature and they are talking about the intrinsic vapor pressure at this given T.

the one with the lower vP needs a higher temperature to boil

 

[Tokspor]

So, every liquid has its own unique vapor pressures that are proportional to the temperature of the liquid...
So, at 50 degrees, lets say water has a vapor pressure of .5 atm... it is 1 atm at a 100 degrees and boils

HOWEVER, there are other liquids that have a vapor pressure of .2 atm at 50 degrees. So having a lower intrinsic vapor pressure means it will have a higher boiling.

so when they say something has a lower vapor pressure when they're comparing the two substances, they're probably assuming both substances are at the same temperature and they are talking about the intrinsic vapor pressure at this given T.

the one with the lower vP needs a higher temperature to boil

Thanks for both your responses. I think I'm getting it. So when they say that "if you lower the vapor pressure, you increase the boiling point," they're really saying "if you lower the effect of temperature on the vapor pressure of a substance, you increase the boiling point," right?

So if you lower the vapor pressure at a given temperature, then you've increased the boiling point. But if you simply lower the temperature, the vapor pressure decreases, but because the vapor pressure v. temperature proportion stays the same, the boiling point doesn't change. Am I on the right track?