Question

pcl5 is 40 % dissociated when is 2 atm, it will be 80 % dissociated when pressure is approx ​

Answer 1

hence, pressure is approximately 0.2 atm

PCl5 dissociates into PCl3 and Cl2 as shown below in reaction..

PCl5 ⇔PCl3 + Cl2

at t = 0, 1 0 0

at eql. (1 - d) d d

here, d is degree of dissociation.

so, Kp = p_[PCl3] × p_[Cl2]/p_[PCl5]

= {d/(1 + d)}P × {d/(1 + d)}P/{(1 - d)/(1 + d)}P

= d²P/(1 + d)(1 - d)

= d²P/(1 - d²)

here, Kp is equilibrium constant.

so, P ∝ 1/{d²/(1 - d²)}

i.e., P/2 = [(0.4)²/(1 - 0.4²)]/[(0.8)²/(1 - 0.8²)]

⇒P/2 = [0.16/0.84 ]/[0.64/0.36]

⇒P/2 = (0.16 × 0.36)/(0.84 × 0.64)

⇒P/2 = (0.09)/(0.84) = 9/84

⇒P = 18/84 = 0.21428 atm ≈ 0.2 atm

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Answer 2

0.2 is the right answer

Explanation: