Contradiction between prep books

[Halcyon32]

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In reference to real gas deviation from ideal behavior:
TPR says that the deviation for volume for a real gas is that Vreal<Videal b/c since the molecules of gas do take up volume, this volume reduces the effective volume of the container. This makes sense to me b/c it's also stated that in the ideal gas equation volume is in reference to the volume of the container since ideal gases don't even have any volume
EK says that the deviation for volume for a real gas is that Vreal>Videal b/c the molecules of gas do take up volume and thus that volume must be added to the ideal volume. Why in the world would you add the volume of the molecules to the ideal volume. isn't ideal volume the measure of the volume of the container?
Can you guys help clear up which of these is the right explanation?

 

[ElectricNoogie]

It seems the issue of confusion is which volume each book is referring to. Technically both books are correct.

TPR is referring to the volume available in the container holding the gas. The IGL assumes gas molecules have negligible volume while in reality they do take up space. Thus Ideal V(available in container) > Real V(available in container).

On the flipside, if EK is referring to the actual volume of the molecule, they are correct and Ideal V(molecule) < Real V(molecule). This relationship would also be the case if they meant total volume [Vmolecules + Vcontainer].

Hope this clears things up. Good luck!

 

[Halcyon32]

It seems the issue of confusion is which volume each book is referring to. Technically both books are correct.

TPR is referring to the volume available in the container holding the gas. The IGL assumes gas molecules have negligible volume while in reality they do take up space. Thus Ideal V(available in container) > Real V(available in container).

On the flipside, if EK is referring to the actual volume of the molecule, they are correct and Ideal V(molecule) < Real V(molecule). This relationship would also be the case if they meant total volume [Vmolecules + Vcontainer].

Hope this clears things up. Good luck!

But doesn't ideal V directly refer to the volume of the container. Like when discussing KMT and IGL that distinction is initially made on the outset

 

[ElectricNoogie]

But doesn't ideal V directly refer to the volume of the container. Like when discussing KMT and IGL that distinction is initially made on the outset

I am not sure where you read that the term volume must refer to the volume of the container. If you are using the Van Der Waal's equation then sure, the term is corrected to V-nb to reflect the diminished capacity of the available space. But AFAIK, you can also just as easily discuss the volume of the molecule when talking about IGL and non-ideal values, it's just not the volume referred to in the equation. Does EK tell you to which volume (molecule vs. container) they are referencing? To me is seems that is must be Vmolecule in order for their statement to be correct. The MCAT will often ask you about a topic (i.e. ideal vs non-ideal volume) from multiple angles so you cannot be locked into one memorized law, you must understand what the law means and what implications it has for many properties.

I would check the EK chapter/section again. Which EK books are you using? Which page is this confusion on?

 

[Halcyon32]

I am not sure where you read that the term volume must refer to the volume of the container. If you are using the Van Der Waal's equation then sure, the term is corrected to V-nb to reflect the diminished capacity of the available space. But AFAIK, you can also just as easily discuss the volume of the molecule when talking about IGL and non-ideal values, it's just not the volume referred to in the equation. Does EK tell you to which volume (molecule vs. container) they are referencing? To me is seems that is must be Vmolecule in order for their statement to be correct. The MCAT will often ask you about a topic (i.e. ideal vs non-ideal volume) from multiple angles so you cannot be locked into one memorized law, you must understand what the law means and what implications it has for many properties.

I would check the EK chapter/section again. Which EK books are you using? Which page is this confusion on?

9th edition EK on pg. 155 when it's talking about the rules for KMT it says: "Gas molecules h ave no size, i.e. zero molecular volume (this is not the same as volume of the container, which is considered for an ideal gas)"

then on page 163 is where it says Vreal>Videal since real gases do have volume and you need to add that volume to the volume of the container. That part especially doesn't make sense. I understand the distinction between when Vreal>Videal if its talking about just the volume of the gas and Videal<Vreal if its talking about the volume of the container but why would you add volume of the gas to the container, it's not like the gas is expanding the container.