CBSE Class 12 · 2015 · Delhi · SolutionsShort Answer

What is meant by positive deviations from Raoult's law? Give an example. What is the sign of

Δ_{mi x} H

for positive deviation?

Answer: Vapour pressure higher than Raoult's law predicts; e.g. ethanol + acetone; ΔH_mix is positive.

Solution

In positive deviation the partial and total vapour pressures of the solution are higher than those calculated from Raoult's law, because the A–B attractions are weaker than the A–A and B–B attractions.
Example: ethanol + acetone.
Mixing needs energy to break the stronger like-attractions, so

Δ_{mi x} H > 0

(positive).

CBSE Class 12 Board · 2015 · Delhi · Subjective

Practise more: all CBSE board PYQs on Solutions →

More board questions on Solutions

Isotonic solutions have the same
CBSE 2024View solution →
Van't Hoff factor for Na $_{2}$ SO $_{4} \cdot$ 10H $_{2}$ O solution, assuming complete ionization, is
CBSE 2024View solution →
(a)(i) Ishan's automobile radiator is filled with 1.0 kg of water. How many grams of ethylene glycol (molar mass = 62 g mol $^{- 1}$ ) must Ishan add to get the freezing point of the solution lowered to −2.8°C? (K $_{f}$ for water = 1.86 K kg mol $^{- 1}$ )
(ii) What type of deviation fro …
CBSE 2024View solution →
(b)(i) The boiling point of water at 750 mm Hg pressure is 99.68°C. How much sucrose (molar mass = 342 g mol $^{- 1}$ ) is to be added to 500 g of water so that it boils at 100°C? (K $_{b}$ for water = 0.52 K kg mol $^{- 1}$ )
(ii) State Henry's law and write any one application of it.
CBSE 2024View solution →
Which of the following aqueous solutions will have the highest boiling point?
CBSE 2023View solution →
(i) Why is the boiling point of 1 M NaCl solution more than that of 1 M glucose solution?
(ii) A non-volatile solute 'X' (molar mass = 50 g mol $^{- 1}$ ), when dissolved in 78 g of benzene, reduced its vapour pressure to 90%. Calculate the mass of X dissolved in the solution.
(iii) …
CBSE 2023View solution →