How does kinetic energy of gases relate to their volume?

[Esoremada]

Which of the following statements accounts for the observation that, at 300 K and 10 atm, the molar volume of C2H6(g) is less than that of H2(g)?

A C2H6 molecules are smaller than H2 molecules.
B The average kinetic energy of H2 molecules is greater than that of C2H6 molecules.
C The average kinetic energy of H2 molecules is less than that of C2H6 molecules.
D The intermolecular attractions in C2H6(g) are weaker than they are in H2(g).
*E The intermolecular attractions in C2H6(g) are stronger than they are in H2(g).
E is the correct answer, but it also seems like B is a reasonable answer, doesn't higher kinetic energy make a substance's volume increase? Isn't that why heating things causes them to expand?

 

[Simon Bridge]

Average KE is proportional to temperature right?
T is the same for each sample, therefore...

 

[Esoremada]

Oh, right. Thanks, idk how I missed that.

 

[Simon Bridge]

Lots of people would - that's why the question is asked that way.
The idea is to reward you for reading with brain engaged (almost nobody does that anyway) and for understanding physics.

The "understanding physics" part gives you two possible answers - B and E (which is how you can tell you are doing well BTW) and you have to do a bit more work to figure out what makes one better than the other. I suspect the actual test is whether you realize the relationship between KE and T.

You can do it the other way around, by memorizing stuff, though... but it's harder.

 

[DeeNos]

While it is true that higher kinetic energy can lead to an increase in volume, in this scenario, the intermolecular attractions play a larger role in determining the volume of the gas. At 300 K and 10 atm, both H2 and C2H6 have similar kinetic energies. However, the intermolecular attractions in C2H6 are stronger than those in H2, causing the molecules to be more tightly packed and resulting in a smaller molar volume for C2H6. This is consistent with the observation that at higher pressures, gases tend to have smaller volumes due to increased intermolecular interactions.