is vapor pressure increased or decreased with greater intermolecular attraction

[an1423]

Im doin the destroyer and they are contradicting themselves i think. on number 166, they say if a liquid is heated, vapor pressure is increased but then in the nest questionstates which substance has the greatest vapor pressure and the answer is the one with least molecular weight.???? need clarification????

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[IWantH2O]

Im doin the destroyer and they are contradicting themselves i think. on number 166, they say if a liquid is heated, vapor pressure is increased but then in the nest questionstates which substance has the greatest vapor pressure and the answer is the one with least molecular weight.???? need clarification????

k think of vapor pressure as how easy a substance evaporates..because remember that the bioling point is when vapor pressure is equal to atmospheric pressure...

if liquid is heated then vapor pressure increases because its easier for it to evaporate
a smaller molecule has less intermolecular forces and therefore easier to evaporate thus higher vapor pressure

 

[AndyK]

Imagine vapor pressure as a force that molecules exert as they go from liquid to gas. The higher the temperature of the liquid, the more energy there is for molecules to use to escape from liquid to gas. Remember that boiling point is when vapor pressure equals or exceeds the atmospheric pressure. When you heat water, you increase its vapor pressure until it overcomes atmospheric pressure and boils.

Vapor pressure decreases as intermolecular attraction increases. If the molecules have high attraction to one another, they will not be as willing to enter a gas phase. Compare water and ether: Water can H-bond, and ether can only dipole-dipole bond (which is weaker); comparatively, ether's bp is 35 C and water's is 100 C.

As far as molecular weight is concerned, generally lower MW molecules will have a higher vapor pressure, lower boiling point, etc. but it also depends on the intermolecular attractions (In my water v. ether example, ether has a much higher MW than water, but also has a much higher vapor pressure)

 

[bigasianpianist]

vapor pressure will be higher if intermolecular forces are lower. They are inversely related to each other and vice versa.

Imagine this, if the bonds between the molecules in the liquid are stronger, it'll take more heat to break these bonds apart. If this is the case the vapor pressure will be lower because it takes much longer to boil the liquid. Hence a higher boiling point for a low vapor pressured solution.

If the bonds between the molecules in a solution is weaker, there will be a higher vapor pressure because the amount of heat to break the bonds will be lower, hence a lower boiling point for solutions with higher vapor pressure.