Vapor Pressure

[osimsDDS]

Advertisement - Members don't see this ad

I always get mixed up with vapor pressure, someone PLEASE help.

Is this correct:
When the vapor pressure is high that means that the gas pressure on the liquid is high and therefore liquid atoms will vaporize more easily?
When vapor pressure is low that means that the gas pressure on the liquid is lower and atoms will vaporize less easily?

Now, positive deviation compared to negative deviation....

Positive means that it just sticks to the regular vapor pressure rule where you have a certain solution that deviates the pure substance and therefore it will vaporize at a lower temperature?

Negative deviation means that the impure solution will vaporize at a higher temperature because the intermolecular attractions are stabilized?

IS ALL THIS TRUE?? I always get confused im trying to figure it out once and for all....THANKS

 

[whoaaitzkyle]

I always get mixed up with vapor pressure, someone PLEASE help.

Is this correct:
When the vapor pressure is high that means that the gas pressure on the liquid is high and therefore liquid atoms will vaporize more easily?
When vapor pressure is low that means that the gas pressure on the liquid is lower and atoms will vaporize less easily?

Now, positive deviation compared to negative deviation....

Positive means that it just sticks to the regular vapor pressure rule where you have a certain solution that deviates the pure substance and therefore it will vaporize at a lower temperature?

Negative deviation means that the impure solution will vaporize at a higher temperature because the intermolecular attractions are stabilized?

IS ALL THIS TRUE?? I always get confused im trying to figure it out once and for all....THANKS

I think of vapor pressure this way. Raoult's law says that solute molecules at the surface of the liquid interfere with the escape of solvent molecules into the vapor phase. So therefore, if you have a vapor pressure lowering (by adding solute), the boiling point of the solution is raised and the freezing point is lowered, as compared with the boiling and freezing point of a pure solvent.

 

[arpitpatel86]

what happens with the pure solvent?

 

[osimsDDS]

I think of vapor pressure this way. Raoult's law says that solute molecules at the surface of the liquid interfere with the escape of solvent molecules into the vapor phase. So therefore, if you have a vapor pressure lowering (by adding solute), the boiling point of the solution is raised and the freezing point is lowered, as compared with the boiling and freezing point of a pure solvent.

Is this exactly opposite of what I said? I ALWAYS get confused with this subject....Is there an example someone can give me between positive and negative deviation, how do you know which solute causes which??? thanks

 

[whoaaitzkyle]

what happens with the pure solvent?

All they're trying to say is that the vapor pressure of the solvent decreases as the concentration of the solute increases (inverse relationship). So therefore, as you increase the solute concentration in a pure solvent, the vapor pressure decreases, thereby increasing the boiling point and decreasing the freezing point.


To the OP, sorry, I don't know what positive and negative deviation is referring to. There are plenty of example vapor pressure questions out there I'm sure. I think it's moreso the conceptual understanding what they're looking for, but if you want to satisfy your curiosity (which I totally would do if I were you) just look up some examples on google if you haven't encountered the kind of questions you want in destroyer, achiever, or topscore. gluck!