Calculate Kp at this temperature for the reaction?

Question

A sample of gaseous PCl5 was introduced into an evacuated flask so that the pressure of pure PCl5 would be 0.5800 atm at 526 K.
But, PCl5 decomposes to gaseous PCl3 and Cl2.
At equilibrium the TOTAL pressure in the flask was measured at 0.9744 atm.


PCl5(g) ↔ PCl3(g) + Cl2(g)

Base your calculations on the reaction as written above


Enter a numeric answer only.

Answer 1

Kp= p(Cl2) p(PCl3) / p(PCl5)
At equilibrium p(PCl3)=p(Cl2)
Let x=pressure of PCl3=pressure of PCl5
The pressure of PCl5 is 0.5800-x
Since total pressure is 0.9744=p(PCl5)+p(PCl3)+p(Cl2)=
= 0.5800-x+x+x
x=0.3944 and 0.5800-x=0.1856
Kp=(0.3944)^2/0.1856 = 0.8381 atm