Question

If vapour pressures of pure liquids ‘A’ & ‘B’ are 300 and 800 torr respectively at 25⁰C. When these two liquids are mixed at this temperature to form a solution in which mole percentage of ‘B’ is 92, then the total vapour pressure is observed to be 0.95 atm. Which of the following is true for this solution.

• A. DVmix> 0
• B. DHmix< 0
• C. DVmix = 0
• D. DHmix = 0

Answer 1

Answer: (B)

DHmix< 0

Answer 2

According to Raoult’s law

PT = (0.08 × 300 + 0.92 × 800) torr = (24 + 736) torr = 760 torr = 1 atm

Pexp. = 0.95 atm < 1 atm

Hence solution shows -ve deviation

so $\Delta H _ { \text {mix } }$ < 0, and $\Delta V _ { \text {mix } }$ < 0.