Question

At 250ºC, the equilibrium constant Kp for the reaction PCl5(g) PCl3(g) + Cl2(g)is 1.80. Sufficient PCl5 is put into a reaction vessel to give an initial pressure of 2.74atm at 250ºC. Calculate the pressure of PCl5 after the system has reached equilibrium

Answer 1

The balanced chemical equation for the reaction is:

PCl5(g) ⇋ PCl3(g) + Cl2(g)

The equilibrium constant expression for this reaction is:

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

We are given that:

- Kp = 1.80
- P[PCl5] = 2.74 atm

We need to find the pressure of PCl5 after the system has reached equilibrium. Let's assume that the equilibrium pressure of PCl5 is x atm.

At equilibrium, the partial pressures of PCl3 and Cl2 are related to the equilibrium pressure of PCl5 by the stoichiometry of the reaction:

P[PCl3] = x atm
P[Cl2] = x atm

We can now substitute these values into the equilibrium constant expression and solve for x:

1.80 = (x * x)/2.74
x^2 = 4.8972
x = 2.210 atm

Therefore, the pressure of PCl5 at equilibrium is 2.210 atm.