Question

At 473 K, equilibrium constant Kc for decomposition of phosphorus pentachloride, PCl₅ is 8.3 ×10^-3 . If decomposition is depicted as, 

         ∆_rH° = 124.0 kJmol^–1 

a) Write an expression for K_c for the reaction. 

b) What is the value of K_c for the reverse reaction at the same temperature? 

c) What would be the effect on K_c if 

(i) more PCl₅ is added 

(ii) pressure is increased? 

(iii) The temperature is increased? 

Answer 1

(a) 

(b) Value of K_c for the reverse reaction at the same temperature is: 

(c) (i) Kc would remain the same because in this case, the temperature remains the same. 

(ii) Kc is constant at constant temperature. Thus, in this case, K_c would not change. 

(iii)In an endothermic reaction, the value of K_c increases with an increase in temperature. Since the given reaction in an endothermic reaction, the value of K_c will increase if the temperature is increased.