Ideal Gas question, can someone help?

[theunremarkable]

---

Members don't see this ad.

A Kaplan question states:

For any given substance at a pressure of 50 atm and a temperature of 30 K, which of the following statements is most likely accurate?

The answer apparently is: The volume of the substance is much less than that predicted by PV = nRT. And they explained it as: The condenses phases of solids and liquids are more dense than gases and thus occupy a smaller volume for a given mass.

I choose an alternate answer which said: The volume of the substance is slightly greater than that predicted by PV = nRT. Because under non-ideal conditions the real volume of a gas is larger than the ideal volume because in a compressed state volume of each molecules is apparent.

 

[BrokenGlass]

A Kaplan question states:

For any given substance at a pressure of 50 atm and a temperature of 30 K, which of the following statements is most likely accurate?

The answer apparently is: The volume of the substance is much less than that predicted by PV = nRT. And they explained it as: The condenses phases of solids and liquids are more dense than gases and thus occupy a smaller volume for a given mass.

I choose an alternate answer which said: The volume of the substance is slightly greater than that predicted by PV = nRT. Because under non-ideal conditions the real volume of a gas is larger than the ideal volume because in a compressed state volume of each molecules is apparent.

30K is a very low temperature, damn near absolute zero (absolute zero is 0 Kelvin). So the substance is pretty much frozen at 30 Kelvin. So it doesn't behave like an ideal gas.

 

[theunremarkable]

Yeah, right, it doesn't behave like an ideal gas so you have to assume that the volume of the molecules have to be taken into consideration.

 

[RoadRunner17]

I'll take a crack at it... in this scenario, the particles of that gas are compressed by the high pressure of 50 atm, and the temperature is quite low at 30K. So:

Fact: At a significantly high pressure, individual particles are much closer together, allowing intermolecular attractions to come into play. In an ideal gas, it is assumed that intermolecular attractions are non-existent.

Fact: The temperature is significantly low, so the average velocity of the individual particles become less significant compared to intermolecular attractions.

Fact: When intermolecular attractions are significant, by definition we expect to be dealing with solids and liquids rather than gases, which have very low intermolecular attraction between its constituent particles.

Taking these facts into consideration, intermolecular attractions are quite significant, and therefore, you would expect a smaller volume compared to an ideal gas, where intermolecular attractions are supposed to be negligible. Also, solids and liquids tend to be more dense than gas, which signifies a smaller volume.

Conclusion: The volume of the substance will be less than that predicted by the Ideal Gas law of PV = nRT due to the high pressure and low temperature causing intermolecular forces to become a large factor. Additionally, we have the likelihood of the substance being a solid or liquid as opposed to gas for most substances (consult a phase diagram for any substance if you are unclear on this) due to the conditions as well as the significance of intermolecular forces.

Hope this made sense. Let me know if you have any questions. Good luck with your studies!

 

[theunremarkable]

Okay, that makes sense. So I guess the volume of the molecules, which is present in a nonideal situation is not the way to think about it because I am dealing with solids.

I guess I was confused because of the V real > V ideal and P ideal > P real statements.