Two liquids A and B ( $P_{A}^{0} = 200$ torr, $P_{B}^{0} = 100$ torr) are mixed in equimolar amounts. The measured total vapour pressure is $170$ torr. Which statements are correct?

Answer: A, B, C

Ideal pressure

= 0.5 \times 200 + 0.5 \times 100 = 150

torr, so the 150 torr statement is correct. Measured

170 > 150

means positive deviation. Positive deviation arises from weaker A-B attractions, so mixing absorbs heat (

Δ H_{mi x} > 0

). Stronger A-B attractions would be the case for negative deviation, so that statement is wrong.