The equilibrium constant (K p) for the interconversion of PCl 5 and PCl 3 is 0.0121: PCl5 (g) → PCl3 (g) + Cl2 (g)
A vessel is charged with PCl 5 giving an initial pressure of 0.123 atm and yields PCl 3 and Cl 2. At equilibrium, the partial pressure of PCl 3 is atm.
A) 0.0782.
B) 0.0455.
C) 0.0908.
D) 0.0330.
E) 0.123.

At equilibrium, the partial pressure of is 0.0330 atm.

Explanation:

The partial pressure of is equal to the partial pressure of . Hence, let us assume that x quantity of is decomposed and gives x quantity of and x quantity of .

Therefore, at equilibrium the species along with their partial pressures are as follows.

At equilibrium:  0.123-x          x              x

Now, expression for of this reaction is as follows.

Thus, we can conclude that at equilibrium, the partial pressure of is 0.0330 atm.