NEET 2019 Odisha · ChemistryPrevious Year Question

Which of the following statements is correct regarding a solution of two compounds A and B exhibiting positive deviation from ideal behaviour?

Answer: (A) Intermolecular attractive forces between A-A and B-B are stronger than those between A-B.. \textbf{Answer:} (A) Intermolecular attractive forces between A-A and B-B are stronger than those between A-B.

A.Intermolecular attractive forces between A-A and B-B are stronger than those between A-B.✓
B. $Δ_{mi x} H = 0$ at constant T and P
C. $Δ_{mi x} V = 0$ at constant T and P
D.Intermolecular attractive forces between A-A and B-B are equal to those between A-B.

Correct Answer

(A) Intermolecular attractive forces between A-A and B-B are stronger than those between A-B.

Solution & Explanation

\textbf{Answer:} (A) Intermolecular attractive forces between A-A and B-B are stronger than those between A-B. \textbf{Solution:} In positive deviation from Raoult's law, the A-B interactions are \textbf{weaker} than the A-A and B-B interactions. Molecules escape more easily, so vapour pressure rises above the ideal value. For such non-ideal solutions $Δ_{mi x} H > 0$ (endothermic) and $Δ_{mi x} V > 0$ , so options B and C (which describe ideal behaviour) are wrong. Option D describes an ideal solution. Hence the correct statement is (A).

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