Help on Kp please?

Question

I am doing some work and im stuck on this question on kp can some1 plz help as I have a test tommorrow so a worked solution would really help me

In the gas phase PCL5 under goes thermal dissociation

PCl5 ----> PCl3 +Cl2 (note. reaction is reversible)

At a certain temperature, and at a total pressure of 3atm, 60% of the PCl5 originally present has dissociated when equilibrium is attained. Calculate the partial pressures of the gases at equilibrium and work out the value of Kp

Thankyou

Answer 1

Let the partial pressures of the substances be denoted P(PCl5), P(PCl3), and P(Cl2)

Kp = P(PCl3)*P(Cl2)/P(PCl5)

After the smoke clears, P(PCl5) = 3atm - 60%(3atm) = 1.2atm

P(PCl3) = P(Cl2) = 1.8atm

Kp = (1.8)(1.8)/(1.2) = 2.7