Ideal gas vs Real gas

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Ideal gas vs Real gas

Post by simsimjoey » Sun Dec 10, 2017 1:06 am

Hi, I have a question about question 10 on chapter 22 from the review book.

The question asks, "compared to an ideal gas, a real gas would have..."

The answer here says b, which is smaller volume than predicted at lower temperatures and high pressure. Correct me if I'm wrong but as far as I know

Ideal gas model become inapplicable at high pressures and low temperatures
- High pressure : volume of particles no longer negligible —> volume of a real gas is larger than the expected ideal
- Low temperature : particles move slowly enough to interact —> volume of a real gas smaller than the expected ideal

They can have counteractive effect on volume, so shouldn't i use van der waal's equation if I were to solve this out...?

Thnx in advnace
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Re: Ideal gas vs Real gas

Post by Administrator » Sun Dec 10, 2017 4:28 pm

Hi simsimjoey, thank you for posting your question!

You are correct: real gases deviate from ideal gas behavior at high pressures and low temperatures. At high pressures, the volume of real gases is larger than predicted, as ideal gases are assumed to have no volume while real gas molecules do have a small amount of volume. At low temperatures, the volume of real gases is smaller than predicted because the attractive intermolecular forces are no longer negligible when gas molecules move more slowly, and thus the distance between molecules decreases, whereas ideal gases are assumed to have no intermolecular interactions.

You're correct in that in such a case, we would have to use the van der Waal's equation to determine which would variable would have a greater effect, but you won't be asked to make that kind of calculation on the PCAT, and we would certainly need more information.

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Good luck studying!
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