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 $