Chemistry Question + Answer

[The Law]

Thanks avenir, our hero. I realize that vapour A is gonna evaporate, and vapour B because of Raoult's law is only 90% of vapour A, but will equilibrium try to make the two equal? I knew that B would get more solvent, just because it does try to balance them out... but I am confused as to when it would stop doing it. Equilibrium doesn't have to keep the two vapour pressures equal does it... it's just forward rxn = reverse rxn... so I don't know what I am missing here.

[eng_dude786]

yea ...my thoughts exactly. I just thought "enough" would go until it reaches equilibrium.

[avenir001]

Thanks avenir, our hero. I realize that vapour A is gonna evaporate, and vapour B because of Raoult's law is only 90% of vapour A, but will equilibrium try to make the two equal? I knew that B would get more solvent, just because it does try to balance them out... but I am confused as to when it would stop doing it. Equilibrium doesn't have to keep the two vapour pressures equal does it... it's just forward rxn = reverse rxn... so I don't know what I am missing here.

 

ya this question kind of reminds me of colligative properties and osmotic pressure...where a semi-permeable membrane (eg permeable to water but not solute) separates pure water from a solution (water + solute)...and what happens is that pure water starts moving into the solution side by osmosis...but as the solution level goes higher and higher, hydrostatic pressure starts pushing back and at some point stops any net flow of water into the solution side.

hmm here we don't have hydrostatic pressure to worry about...so i'd say all solvent in Beaker A will evaporate and try to dilute the solution in Beaker B...as long as Beaker B is big enough to accommodate it..and as long as the whole closed container is big enough so that the vapour pressure inside the container is lower than or equal to the saturation vapour pressure of the volatile solvent at that temperature...under these conditions, u can have all ur solvent in Beaker B in equilibrium with its vapour throughout the container...but if ur container is too small such that it's oversaturated with vapour at a given temperature, u're gonna have vapour condensing in Beaker A, container walls, etc.

i dunno, that's what i think...prolly too much thinking than is required for the mcat tho

[avenir001]

I realize that vapour A is gonna evaporate

 

LOL..i love lawian english