NEET2026ChemistryChapterActual
A binary solution is prepared by mixing 2 moles of liquid P and 3 moles of liquid Q. At a certain temperature, the vapour pressures of pure P and pure Q are 120 mm Hg and 160 mm Hg, respectively. If the experimentally observed total vapour pressure of the mixture is 155 mm Hg, which of the following statements is correct regarding this solution?
Options
- AThe process of mixing liquids P and Q is exothermic ( H_ mix < 0 ).
- BThe solution is capable of forming a maximum boiling azeotrope.
- CThe intermolecular attractive forces between P and Q are weaker than those in pure P and pure Q.
- DThe volume of the resulting solution is less than the sum of the volumes of the unmixed liquids.
Correct answer
C. The intermolecular attractive forces between P and Q are weaker than those in pure P and pure Q.
Step-by-step solution
Mole fraction of P, x_P = 2 2+3 = 0.4 Mole fraction of Q, x_Q = 3 2+3 = 0.6 According to Raoult's law, the ideal vapour pressure of the solution is: P_ ideal = P_P^ x_P + P_Q^ x_Q P_ ideal = 120 0.4 + 160 0.6 = 48 + 96 = 144 mm Hg The observed vapour pressure is 155 mm Hg , which is greater than the ideal vapour pressure ( 155 > 144 ). This indicates that the solution shows a positive deviation from Raoult's law. For a solution showing positive deviation: 1. The intermolecular attractive forces between the differen