Question

A solution containing components A and B exhibits positive deviation from Raoult?s law only when (1) $\Delta V_{mixing}=+ve$ (2) $\Delta H_{mixing}=-ve$ (3) $A-B$ attraction forces $<A-A$ and $B-B$ attraction forces. (4) $A-B$ attraction forces $>A-A$ and $B-B$ attraction forces.

• A. 1, 2 and 3 are correct.
• B. 1 and 2 are correct.
• C. 2 and 4 are correct.
• D. 1 and 3 are correct.

Answer 1

Answer: (D)

When the $AB$ interaction are weaker than the $AA$ and $BB$ interaction, then solution exhibits positive deviation from Raoult?s law. For such solutions AH mixing is positive because energy is required to break $AA$ or $BB$ attractive forces. On mixing, because the magnitude of intermolecular forces in solution decreases, thus the molecules will be loosely held, hence volume increases ie, $\Delta V_{mixing}=+ve$