Deviations From Ideal Gas

[GTWreck1991]

Hey guys...had a quick question regarding Ideal Gases that wasn't tackled to my liking in similar posts. I understand that ideal gases behave at high T and low P....due to the increased kinetic energy and low pressure resulting in less intermolecular attraction of gas molecules...I also understand that at moderately high pressure and low temperature...the expected volume from the ideal gas law..is greater than the real gas due to the intermolecular forces present at the increased pressure and low temperature. All of this makes sense...my question pertains to extremely high pressure and extremely low temperature. I'm using Kap...and what I've gotten is this...

Moderately high P and low T = gas is smaller than predicted by ideal gas law due to increased intermolecular attractions
Extreme high P and extremely low T = gas is larger than predicted by ideal gas law...due to the fact at such extremes...the volume of the gas particles themselves is bigger than the distance between particles.

So now to my question.....how can we differentiate between the two? Is there a number we should memorize that is considered moderately high vs extreme? And have I understood the above material correctly? Or am I confusing concepts?

Thanks!

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[NicMouse64]

Hey guys...had a quick question regarding Ideal Gases that wasn't tackled to my liking in similar posts. I understand that ideal gases behave at high T and low P....due to the increased kinetic energy and low pressure resulting in less intermolecular attraction of gas molecules...I also understand that at moderately high pressure and low temperature...the expected volume from the ideal gas law..is greater than the real gas due to the intermolecular forces present at the increased pressure and low temperature. All of this makes sense...my question pertains to extremely high pressure and extremely low temperature. I'm using Kap...and what I've gotten is this...

Moderately high P and low T = gas is smaller than predicted by ideal gas law due to increased intermolecular attractions
Extreme high P and extremely low T = gas is larger than predicted by ideal gas law...due to the fact at such extremes...the volume of the gas particles themselves is bigger than the distance between particles.

So now to my question.....how can we differentiate between the two? Is there a number we should memorize that is considered moderately high vs extreme? And have I understood the above material correctly? Or am I confusing concepts?

Thanks!

I am not studying for the mcat but I think this might help....
You have PV=nRT where pressure is 1 ATM (760 torr) and Volume is in Liters. So for my chemistry class we used 1 ATM-L as a normal PV. Anything above 10 is Extremely high, anything below .1 is low. Also note that any of the variables in PV=nRT could be changed to reflect a unit near 1. Also realize that the gas is not "smaller", it just has a smaller volume that it is enclosed in. PV=nRT is really all you need to know, but being able to visualize the intermolecular forces for pressure and temperature should be intuitive. If not think of a bunch of people in a room. The smaller the room the more times you will bump into them. The faster everyone is moving (higher temperature) the more interactions.

 

[sazerac]

You understand the concepts. Distinguishing between partially extreme and really extreme is not very MCAT-like. If you can handle the non-ideal gas law questions in your review system you will be fine. You will most likely get some kind of question that has four explanations of why your gas is not obeying the ideal gas law and you have to pick the correct one (or even more likely, be able to eliminate three bad explanations).

 

[ElectricNoogie]

@sazerac is correct. This kind of nit-picking discrimination is NOT the domain of the MCAT. Similar to how in Biology, if they ask you to make estimations of the percentages of alleles and phenotypes, they allow you to use the Hardy-Weinberg equations without confirming your population is sufficiently "large." The MCAT prefers to test your understanding of concepts and relationships, not "arbitrary" designations. That won't become important until med school ;-)

 

[Blueprint MCAT Tutor]

So now to my question.....how can we differentiate between the two?

Just to follow up on what Anthony mentioned above - don't worry, it won't even be close. If they want "extreme" conditions they'll tell you it's like 200 atm of pressure or like -200ºC temperature.