volume of ideal gas vs real gas

[sixpence]

why does a real gas have a higher volume than an ideal gas? i know that the pressure of a real gas is lower bc intermolecular attractions but i dont know about volume. EK has a one sentence explanaation... Also, can someone clarify exactly what volume we're talking about? I read about free volume and molecular volume and volume of the container? Thanks!

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[dundunham]

Hm, I read in my TPR book it says the real volume is less than the ideal volume because molecules of real gases DO have volume which reduces the effective volume of the container. Also, under Ideal-gas behavior, it says the molecules of an ideal gas are so small compared to the average spacing between them that the molecules themselves take up essentially no volume. And then I read in an explanation that molecules of perfect (ideal) gas take up zero volume. And then another explanation that real gases can never behave as true ideal gasses because 1) their molecules occupy space and 2) their molecules experience attractive intermolecular forces.

Hm.. hope this helps lol

 

[sv3]

i have TPR and Ek and they contradict each other. I have yet to see a clear rule.

I prefer TPR in that when they say an ideal gas virtually takes up no volume, i interpret it as infinite volume, and then it makes sense to me that since a real gas does have volume, the volume of a real gas is less than an ideal gas (why? im not sure exactly as TPR didn't explain this...both TPR and Ek "skirt" around this issue!!). Not sure if my interpretation is right but it fits for me. Otherwise i'd still be banging my head against my desk and I really can't afford to much longer. .......

 

[kobe200LATE]

TPR says that the volume and pressure of a real gas is less than the volume and pressure of an ideal gas because the real gas has intermolecular forces while ideal gases do not. Intermolecular forces cause the molecules to stick together more, preventing them from spreading out further (ie preventing them from increasing their volume) and applying more pressure to the walls of a container (ie less pressure).

 

[chemtopper]

Okay Let me try to help you
It is true that volume of real gases is more than expected volume of the same gas under ideal behavior.
Now here we have to understand it on the basis of two volume
Molecular volume and free volume of the container .
Sum of molecular volume and free volume is the volume of the container or total volume occupied by a gas.
Now in ideal gases we say IMF(intermolecular forces) are negligible and molecules are far away from each other .This leads to assumption that molecular volume of gas is nearly negligible in comparison to total volume.Same is not true with real gases.IMF are not negligible and molecules are attracted to each other.Now we can not neglect molecular volume .
Now apply it on this concept:
Sum of molecular volume and free volume is the total volume occupied by the gas.
Now you see real gases (Total volume) will have more volume because molecular volume is not negligible .Ideal gases, total volume is less because molecular volume is negligible.
That is the reason in real gas equation we apply corrected volumes and pressures
Videal = Vreal- nb
Pideal= Preal + n2a/V2
These are called as the correction terms also.
apply this correction on ideal gas law---PV=nRT
(Preal + n2a/V2)(Vreal- nb )=nRT
The above equation is for real gases.
Now we are interested or we can say gas laws are applied on the volume of the container which is free or the space which is available for gas molecules to move.If we take a fixed and equal volume containers and put same amount of gas in them under ideal and real gas conditions.Than we can say real gases have less free volume to move around and ideal gases have more volume to move around.
So you can see here these two books are talking about two different volumes
Real gas (total volume) > ideal Gas (total volume) for the same amount of gas .
Real Gas(free volume) < ideal gas (free volume)
Gas Law's are applicable on free volume in which molecules are moving.
Effect of temperature and pressure is related with free volume .
In case of ideal gas Free volume of the container = volume of the container.
In case of real gases Free volume of the container < total volume of the container .
I hope this explanation helps you .

 

[dundunham]

nice explanation

 

[sixpence]

thanks!

 

[Vanguard23]

Yeah, EK Chemistry explains this.
Real volume is greater because it operates under the principle that the molecules *take up space*. Especially at lower temperatures where the molecules are closer together. That's why low temperatures cause positive deviations in volume from ideal gases.
Real pressure is less because of intermolecular forces pulling the molecules together before they hit the container surface(reducing the effect of pressure). Think of it like a mentally ill kid with a bungee attached to his torso while running into a wall. Which will hit the wall with greater force(P=F/A), the mentally ill kid with the bungee attached or the one without the bungee attached?
Hope that helps because from this day forward everyone reading this will associate PV problems with these disadvantaged children.