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- Dec 31, 2014
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Many questions have been asked, but none for this specific question. It is not a symantics question either (ie not matter of defining Vreal vs Videal)
So the question is from TBR gen chem passage, where essentially a given amount of argon gas occupies:
10 cm in a glass tube @1atm
5 cm @ 2atm (via addition of 76 cm Hh)
And then 3.3 cm (via addn of another 76cm Hg)
These measurements refer to the "height of the gas" ie its length component of volume, as the tube has constant cross sectional area.
Now the question is
31.)
If a gas made up of molecules rather than atoms were substituted for argon gas in the first experiment,what should be observed for the heights of the gas in the left side of the tube in each of the trials?
A) 100mm, 53mm, 35mm
B) 100mm, 53mm, 31mm
C) 100mm, 47mm, 35mm
D) 100mm, 47 mm, 31mm
I chose D based on the reasoning that at moderately high pressure, a gas is more likely to deviate from intermolecular forces (attractive was my guess thus reducing the volume), whereas at very high pressure the molecular volume becomes significant and the observed volume is greater than expected.
TBR chose A based on the following logic:
"Because molecules are larger than atoms, they are less compressible than atoms. In other words as you compress molecules, they interact (collide and repel) more than atoms interact, so molecules cannot be compressed as easily as atoms. This means the volume of the molecular gas does not decrease as much as it does for argon gas when a pressure of equal magnitude is applied to both systems. This means that the volume of the molecular gas is greater than the volume of the argon gas. The radius of the tube is uniform, so for the volume to be greater the height must be greater. The heights when using a molecular gas are greater than 50mm in the second manometer and greater than 33mm in the third manometer. This is best described in choice A"
I have reviewed other posts, explanations given, and this one doesnt seem to align... First of all, my mcat intuition after reviewing the material tells me these pressure increases (1,2,3atm) wouldn't even be significant enough to affect the observed volume. But then, the idea that molecular gases are larger, therefore less compressible seems irrelevant to the question, considering they attribute this to intermolecular forces. I was under the impression these intermolecular forces could be attractive or repulsive, and that attractive seemed to be the general go-to unless clearly indicated.
Someone who knows their stuff please explain this one for me. Thanks in advance
So the question is from TBR gen chem passage, where essentially a given amount of argon gas occupies:
10 cm in a glass tube @1atm
5 cm @ 2atm (via addition of 76 cm Hh)
And then 3.3 cm (via addn of another 76cm Hg)
These measurements refer to the "height of the gas" ie its length component of volume, as the tube has constant cross sectional area.
Now the question is
31.)
If a gas made up of molecules rather than atoms were substituted for argon gas in the first experiment,what should be observed for the heights of the gas in the left side of the tube in each of the trials?
A) 100mm, 53mm, 35mm
B) 100mm, 53mm, 31mm
C) 100mm, 47mm, 35mm
D) 100mm, 47 mm, 31mm
I chose D based on the reasoning that at moderately high pressure, a gas is more likely to deviate from intermolecular forces (attractive was my guess thus reducing the volume), whereas at very high pressure the molecular volume becomes significant and the observed volume is greater than expected.
TBR chose A based on the following logic:
"Because molecules are larger than atoms, they are less compressible than atoms. In other words as you compress molecules, they interact (collide and repel) more than atoms interact, so molecules cannot be compressed as easily as atoms. This means the volume of the molecular gas does not decrease as much as it does for argon gas when a pressure of equal magnitude is applied to both systems. This means that the volume of the molecular gas is greater than the volume of the argon gas. The radius of the tube is uniform, so for the volume to be greater the height must be greater. The heights when using a molecular gas are greater than 50mm in the second manometer and greater than 33mm in the third manometer. This is best described in choice A"
I have reviewed other posts, explanations given, and this one doesnt seem to align... First of all, my mcat intuition after reviewing the material tells me these pressure increases (1,2,3atm) wouldn't even be significant enough to affect the observed volume. But then, the idea that molecular gases are larger, therefore less compressible seems irrelevant to the question, considering they attribute this to intermolecular forces. I was under the impression these intermolecular forces could be attractive or repulsive, and that attractive seemed to be the general go-to unless clearly indicated.
Someone who knows their stuff please explain this one for me. Thanks in advance
