For two molecule, 1 and 2, we know that ?1 is less than ?2. What can we definitively say?

Question

A. A mole of molecule 1 will display less non-ideal gas behavior than a mole of molecule 2.
B. Molecule 1 has higher vapor pressures at all temperatures than molecule 2.
C. Molecule 1 is less sphere-shaped than molecule 2.
D. The two molecules are different.
E. None of these is definitively true, based on just the given information.

Answer 1

A. Incorrect. The acentric factor can be used to quantify vapor pressures, but does not directly tell you anything about the Z of the compound in the vapor phase.
B. Incorrect. Acentric factors relatereduced vapor pressures to reduced temperatures. Without knowing the values of the critical temperatures, it is impossible to determine which compound has higher vapor pressures.
C. Incorrect. If both acentric factors are positive and ?1 is smaller, then ?1 is closer to zero and we’d expect compound 1 to be more spherical. This is not actually the definition of “acentric factor” however, just an observation that is usually true.
D. Correct. Because the acentric factor is a physical property of the molecule, different acentric factors must indicate different species. The reverse is not true: two different molecules could share essentially the same acentric factor.
E. Incorrect. One statement is definitely accurate.