Van der Waals pt 2...clarification needed:

[Transformers]

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This is a TWO PART QUESTION:

First, I know what the effects of temperature and pressure such that high T and low P = ideal conditions; but what about the effects of volume? Is high V good for ideal gas conditions?

Second, Look at the following:
http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch4/graphics/4_19fig.gif

Based on this, I wanted to clarify two points, according to the site:
. .à As the pressure of CO2 increases the van der Waals equation initially gives pressures that are smaller than the ideal gas equation, as shown in the figure below, because of the strong force of attraction between CO2 molecules. (notice the DIP)
. .à The van der Waals equation gives results that are larger than the ideal gas equation at very high pressures, as shown in the figure above, because of the volume occupied by the CO2 molecules.
THUS: The size of the particles becomes more significant than
intermolecular forces.


Can someone explain this PV vs. P graph to me and these points, since I am confused.

 

[PiBond]

Graph just shows the ideal gas behavior being constant, whereas the real gas deviates due to the fact that when we increase pressure a lot the volume of the gas becomes significant. Therefore our PV value increases relative to the ideal gas behavior.

 

[Silverfalcon]

Hello!

1) Know following properties for ideal behavior and non-ideal behavior of gases.
Ideal Behavior
Low External Pressure
High Volume
High Temperature
Non-Ideal Behavior
High External Pressure
Low Volume
Low Temperature

So, yes, high V is expected for ideal behavior of gases.

2) You basically explained the graph correctly (I think). Basically, the non-ideal behavior, or say, real behavior of gases, differs at temperatures because ideal gas assumes that atoms/molecules of gases are so small that they do not occupy any volume and two, that they are so far apart that they have negligible interactions.

The real gas behavior takes into these assumptions into the account, so that's why the real gas behavior (or non-ideal gas behavior - I keep using them interchangeably so follow along) deviates from the ideal gas behavior graph.

 

[BerkReviewTeach]

So, yes, high V is expected for ideal behavior of gases.

I'm curious where you read this. In looking through a significant number of general chemsitry resources, never once did any one of them mention any correlation between volume and ideality.

Your including of volume makes common sense, but if it's not listed in any textbook, I'd be hesitant to refer to it as a condition, given that the test writers might not consider it.

Ideal behavior depends on intermolecular forces and atomic (or molecular) size. High temperature allows particles to overcome any forces and low pressure implies very few collisions, and therefore very little intermolecular interactions. Those two are well-documented conditions for ideality.

A larger volume can be thought of as giving the particles a wider berth, and therefore reducing their interactions, making it more ideal. But that could also be achieved by reducing the number of particles (lowering the moles) or it's already implied by the low pressure. Im curious if redundancy is why it's not listed as a condition in text books.

It would seem (and fitting with what you described), high T, low P, high V, and low n would lead to the most ideal conditions. But I can't find any source that says anything more than high T, low P, and inert gas.

 

[kentavr]

>>I'm curious where you read this.
I don't think it is mentioned anywhere directly since T,P,n mostly define the state for ideal gas. However, the correct word will be density instead of volume for non-ideal gas.
If you take a look at Van-der-Waals equation (for example here http://en.wikipedia.org/wiki/Van_der_Waals_equation) you will see a parameter v, which is a volume per molecule. It is compared with volume of the molecule itself and raise the non-ideal terms in equation.

 

[Silverfalcon]

I'm curious where you read this. In looking through a significant number of general chemsitry resources, never once did any one of them mention any correlation between volume and ideality.

Your including of volume makes common sense, but if it's not listed in any textbook, I'd be hesitant to refer to it as a condition, given that the test writers might not consider it.

Ideal behavior depends on intermolecular forces and atomic (or molecular) size. High temperature allows particles to overcome any forces and low pressure implies very few collisions, and therefore very little intermolecular interactions. Those two are well-documented conditions for ideality.

A larger volume can be thought of as giving the particles a wider berth, and therefore reducing their interactions, making it more ideal. But that could also be achieved by reducing the number of particles (lowering the moles) or it's already implied by the low pressure. Im curious if redundancy is why it's not listed as a condition in text books.

It would seem (and fitting with what you described), high T, low P, high V, and low n would lead to the most ideal conditions. But I can't find any source that says anything more than high T, low P, and inert gas.

That's a good point... It was from my notes, and I just got my chemistry exam back today, and this was one of the questions (I got two questions right because I chose to answer this question.. haha 😀):

Q: Which of the following conditions are most conducive to ideal behavior in a gas?
A (I put this & it's correct): High temperature, low pressure, high volume

So, I did have right stuffs in the notes. As far as my wording for "expected," I'm not sure about that. It does make sense, as you noted, to have high volume though. I feel that because high P is a really well-known characteristic, high V somewhat follows that as an "unofficial" characteristic, maybe?