Equilibrium questions

Question

Phosphorus trichloride gas and chlorine gas react to form phosphorus pentachloride gas: PCl3(g) + Cl2(g) ↔ PCl5(g). A 7.5L gas vessel is charged with a mixture of PCl3(g) and Cl2(g), which is allowed to equilibrate at 450K. At equilibrium the partial pressures of the three gases are PPCl3 = 0.124atm, PCl2 = 0.157atm, and PPCl5 = 1.30atm. a) What is the value of Kp at this temperature? b) Does the equilibrium favor reactants or products? c) Calculate Kc for this reaction at 450K.

Answer 1

PCl₃(g) + Cl₂(g) <==> PCl₅(g)

0.124 atm...0.157 atm......1.30 atm

(a). Kp = (P_PCl5) / (P_PCl3)(P_Cl2) = 1.30 / (0.124)(0.157)

Kp = 1.30 / 0.0195

Kp = 66.7

(b). Equilibrium is >> 1 so it clearly favors products.

(c). Kp = Kc (RT)^∆n

Kp = 66.7

Kc = ?

R = 00821 Latm/Kmol

T = temp in Kelvin = 450K

∆n = change in number of moles = 1 - 2 = -1

Solve for Kc:

66.7 = Kc (0.0821 x 450)^-1

66.7 = Kc (36.95)^-1

66.7 = Kc x 0.0271

Kc = 2461