A binary liquid mixture shows positive deviation from Raoult's law. Which pair of signs is correct for the mixing process?

A $Δ_{mix} H < 0$ and $Δ_{mix} V < 0$
B $Δ_{mix} H > 0$ and $Δ_{mix} V < 0$
C $Δ_{mix} H = 0$ and $Δ_{mix} V > 0$
D $Δ_{mix} H > 0$ and $Δ_{mix} V > 0$

Answer: D

In positive deviation the A-B attractions are weaker than the A-A and B-B attractions, so molecules escape more easily and the vapour pressure is higher than the ideal value. Weaker interactions mean heat is absorbed and the volume expands on mixing. Hence

Δ_{mix} H > 0

and

Δ_{mix} V > 0

Practice Solutions and Colligative Properties More on Raoult's law, ideal and non-ideal solutions, azeotropes

Previous questionNext question

More questions on Raoult's law, ideal and non-ideal solutions, azeotropes

Liquids A and B form an ideal solution with pure-liquid vapour pressures p_A^0=400 torr and p_B^0=120 torr at a given temperature. A liquid ... JEE Advanced level
The vapour pressure of pure water at 25 degC is 23.8 mmHg. A solution is prepared by dissolving 90 g of glucose (molar mass 180 g mol^-1) in... JEE Main level
What mass of glucose (molar mass 180 g mol^-1) must be dissolved in 250 g of water (molar mass 18 g mol^-1) to lower the vapour pressure of ... JEE Main level
Two liquids A and B form an ideal solution. The vapour pressures of pure A and pure B at 300 K are 150 torr and 60 torr. For a liquid with m... JEE Main level
Which of the following pairs of liquids is expected to form a nearly ideal solution? NEET level
At 300 K pure liquid A and pure liquid B have vapour pressures 300 torr and 200 torr. An equimolar liquid mixture of A and B is found experi... JEE Main level