Kaplan FL#7 Physical Sciences Q.10

[rcohen26]

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I'm not understanding the answer the this question:

The compressibility ratio is given as Z=(pv)/(nrT).

The question asks what will happen to the compressibility ratio (Z) if IMF increases:

If IMF increases then the gases should be acting more REAL than IDEAL. Therefore, volume should decrease while pressure increases. I don't see why pressure would decrease. That would imply IDEAL conditions and low IMF. Any ideas?

 

[Halfling]

I'm not understanding the answer the this question:

The compressibility ratio is given as Z=(pv)/(nrT).

The question asks what will happen to the compressibility ratio (Z) if IMF increases:

If IMF increases then the gases should be acting more REAL than IDEAL. Therefore, volume should decrease while pressure increases. I don't see why pressure would decrease. That would imply IDEAL conditions and low IMF. Any ideas?

nice question 🙂

So, this is correct:
"If IMF increases then the gases should be acting more REAL than IDEAL."

This is wrong:
"Therefore, volume should decrease while pressure increases. I don't see why pressure would decrease."

Why?
The question states that the attractive forces increase. If the attractive forces increase the pressure on the wall of the container will decrease. (The "pull" on each molecule felt by another molecule in the vicinity will increase. This means the velocity (and momentum) of each molecule that collides with the wall of the container will be lower.)
If the pressure decreases it would be easier to compress so the ratio would decrease.

** When we talk about IMF in class we normally talk about repulsive forces between molecules (they have an electron cloud which would probably repel each other). In this case they talk about attractive forces. I'm assuming this confused you? lol

The pressure on each molecule molecule (number of collusion) would increase. (I don't think they ask us about molecule pressure or anything in the MCAT).