Vapor Pressure Elevation?

[sv3]

Why is it assumed that adding a solute will decrease the vapour pressure of the solution? I get the formula and that solutes "anchor" down the solvent molecules making it harder to vaporize....but lets say the solute has a higher pure vapor pressure than the solvent, wouldnt you then be increasing the overall vapour pressure? Or is this impossible for some reason?

The questions i've seen always have the solvent with a higher pure vapour pressure but just wondering if it is reversed......then isnt this vapour pressure elevation? Wondering where I'm wrong with my conceptual thinking....

thanks

steve

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[thebillsfan]

Why is it assumed that adding a solute will decrease the vapour pressure of the solution? I get the formula and that solutes "anchor" down the solvent molecules making it harder to vaporize....but lets say the solute has a higher pure vapor pressure than the solvent, wouldnt you then be increasing the overall vapour pressure? Or is this impossible for some reason?

The questions i've seen always have the solvent with a higher pure vapour pressure but just wondering if it is reversed......then isnt this vapour pressure elevation? Wondering where I'm wrong with my conceptual thinking....

thanks

steve

yup steve, youre right. this question i believe was actually asked yesterday. the assumption that you were talking about is when its a nonvolatile solute. if its a volatile solute, then it depends on the relative vapor pressures of the two solvents. at least, thats what i gathered from ek

 

[sv3]

yup steve, youre right. this question i believe was actually asked yesterday. the assumption that you were talking about is when its a nonvolatile solute. if its a volatile solute, then it depends on the relative vapor pressures of the two solvents. at least, thats what i gathered from ek

Ah thanks. I'm stressed for time so stopped using Ek and only using TPR down the stretch but i'll look this up

cheers

 

[G1SG2]

Yeah, it depends on whether or not the solute is nonvolatile.

 

[thebillsfan]

yeah, look it up to learn it more fully, its very useful

 

[SolidWater]

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