Multiple choice

Total vapour pressure of mixture of $1$ mol X( $P^o{_X} =150\ torr)$ and 2 mol $Y$ ($P^0{_Y}= 300 torr$) is $240$ torr. In this case:

  1. there is a negative deviation from Raoult's law

  2. there is positive deviation from Raoult's law

  3. there is no deviation from Rault's law

  4. cannot be decided
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A Correct answer
Explanation

Mole fractions: X = 1/3, Y = 2/3. Raoult's law expected pressure = (1/3)*150 + (2/3)*300 = 50 + 200 = 250 torr. Actual pressure is 240 torr. Since 240 < 250, there is a negative deviation.

AI explanation

Using Raoult's law, we calculate the expected total vapor pressure for an ideal mixture by finding the sum of the products of their mole fractions and pure vapor pressures. The mole fraction of X is 1/3 and the mole fraction of Y is 2/3, giving an ideal pressure of (1/3 times 150 torr) plus (2/3 times 300 torr), which equals 250 torr. Since the observed vapor pressure of 240 torr is lower than the ideal pressure of 250 torr, there is a negative deviation from Raoult's law.

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