Question

The reaction pcl3(g)+cl2(g)←−→pcl5(g) has kp=0.0870 at 300 ∘c. a flask is charged with 0.50atmpcl3, 0.50atmcl2, and 0.20atmpcl5 at this temperature. part a use the reaction quotient to determine the direction the reaction must proceed in order to reach equilibrium.

Answer 1

The question only asks regarding the direction of the equilibrium reaction. The general expression of Kp is:

Kp = [PCl₅]/[PCl₃][Cl₂]

The higher the value of K (greater than 1), the more spontaneous the reaction (favors the product side). Otherwise, it favors the reactant side. Since Kp = 0.087 which is less than 1, the direction favors the forward reaction towards the product side.

Answer 2

Given, equilibrium constant  Kp = 0.0870

Pressure of PCl₃ = 0.50 atm

Pressure of Cl₂ =  0.50 atm

Pressure of PCl₅ = 0.20 atm

Reaction quotient, Q =  $\frac{0.20 atm}{0.50 atm x 0.50 atm}$

Q = 0.8

Q > K, net reaction is to the left

Q= K, no net reaction

Q < K, net reaction is to the right

Q = 0.8  and Kp = 0.0870

Q is greater than K, so the net reaction is to the left or to the reactant side.

Therefore, the reaction must proceed to the left or to the reactant side in order to reach equilibrium.