In 20 moles of liquid A, 2 moles of liquid B are added. Just after addition, B starts dissociating into C and D following first order kinetics according to given chemical reaction. B → C + 2D C is liquid but D is nonvolatile soluble solute. If the half life of B is 20 min then calculate vapour pressure (in cm of Hg) of solution after 40 min of starting the reaction. [Given : P°A = 40 cm of Hg, P°B = 30 cm of Hg, P°C = 50 cm of Hg ]

Engineering

Chemistry

Raoult Law and Vapour Pressure

Question

In 20 moles of liquid A, 2 moles of liquid B are added. Just after addition, B starts dissociating into C and D following first order kinetics according to given chemical reaction.

B → C + 2D

C is liquid but D is nonvolatile soluble solute. If the half life of B is 20 min then calculate vapour pressure (in cm of Hg) of solution after 40 min of starting the reaction.

[Given : P°_A = 40 cm of Hg, P°_B = 30 cm of Hg, P°_C = 50 cm of Hg ]

37.4

34.4

35.6

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B → C + 2D

t = 0 2 mol 0 0

t = 40 0.5 mol 1.5 mol 3 mol

P = X_A · P°_A + X_B · P°_B+ X_C · P°_C

$= \frac{20}{25} \times 40 + \frac{0 .5}{25} \times 30 + \frac{1 .5}{25} \times 50 = 35 .6 cm of Hg$

Total moles = 20 + 0.5 + 1.5 + 3 = 25