ideal volume and pressure

[jon0013]

so i know real pressure is less than ideal pressure

the question is what about volume
princeton review says real volume less than ideal volume

EK says ideal volume is less than real volume..whats going on?

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[VPDcurt]

High pressures and low temps cause deviations from the ideal. Therefore, I would say that real volume is less than ideal volume.

 

[bella_dottoressa]

I think it's that real volume is greater than ideal volume because one of the rules of ideal gases is that you assume the molecules have zero volume.

 

[VPDcurt]

I think it's that real volume is greater than ideal volume because one of the rules of ideal gases is that you assume the molecules have zero volume.

You assume that the molecules of the gas are so small that they essentially take up no volume, but the gas still has a volume. This is an assumption because the space in between each gas molecule is so large compared to the size of each gas molecule.

 

[willthatsall]

At moderately high pressure, real gas has lower volume than would be predicted because of the attractive forces between the molecules. At very high pressures, the volume is greater than would be predicted because the actual size of the molecules begins to play a bigger role.

 

[DieselPetrolGrl]

if real p is more than ideal p and p and v are inversely related i would have guessed that real v is less than true v

same kind of thinking for the other thing..baby i dont mem-or-ize..i the-or-ize!
(now if only i was good at it)

 

[VPDcurt]

Molecular weight also plays a role - larger MWs deviate more and a diatomic gas will deviate more than a monatomic gas.

 

[jon0013]

the consensus is real P is less than ideal P..so based on Diesol Girl's reasoning (good work)...Real V is more than ideal V...

its disturbing that i'm finding discrepancies in the two texts..Also if anyone has TPR, do you know whats going on with Ex 5-7

A soln is formed mixing 0.6 mol Benzene with 0.2 mole toulene. At the temp of the soln, the vapor pressure of pure benzene is 96 torr and vp of pure toulene is 28 torr...

now the mole fraction of toulene is 1/4...

using the equation for vp depression Pb=-XtPb=-(1/4)(96)=24 torr

however when you use dalton's law you get total pressure
3/4(96)+1/4(28)=72+7=79...the original pressure of benzene is 96..the calculated depression is 24..why is the dalton's total pressure 79 as opposed to 72???

thanks

 

[DieselPetrolGrl]

yes this is one of the rules of the kinetic theory - they are esentially hypothesized as massless & volumeless arnt they?

 

[willthatsall]

the consensus is real P is less than ideal P..so based on Diesol Girl's reasoning (good work)...Real V is more than ideal V...

its disturbing that i'm finding discrepancies in the two texts..Also if anyone has TPR, do you know whats going on with Ex 5-7

A soln is formed mixing 0.6 mol Benzene with 0.2 mole toulene. At the temp of the soln, the vapor pressure of pure benzene is 96 torr and vp of pure toulene is 28 torr...

now the mole fraction of toulene is 1/4...

using the equation for vp depression Pb=-XtPb=-(1/4)(96)=24 torr

however when you use dalton's law you get total pressure
3/4(96)+1/4(28)=72+7=79...the original pressure of benzene is 96..the calculated depression is 24..why is the dalton's total pressure 79 as opposed to 72???

thanks

Did you see what I wrote about the volume? Whether the real volume is less than or greater than the ideal volume depends on the exact pressure. Mod high pressure = less volume than expected due to attractive forces. Very high pressure = higher volume than expected due to physical size of the molecules.