Question

At 473 K, the equilibrium constant K_C for the decomposition of phosphorus pentachioride (PCl₅) is 8.3 x 10^-3. If decomposition proceeds as:

PCI₅(g) ⇌ PCI₃(g) + Cl₂(g); 

∆H = + 124.0 kJ mol^-1

1. Write an expression for K. for the reaction. 

2. What is the value of K for the reverse reaction at the same temperature. 

3. What would be the effect on K_C if 

• More of PCI₅ is added 
• Temperature is increased.

Answer 1

1. The expression for

2. For reverse reaction

3.(i) By adding more of PCI₅, value of K_C will remain constant because there is no change in temperature. 

(ii) By increasing the temperature the forward reaction will be favoured since it is endotherniic in nature. 

Therefore, the value of equilibrium constant will increase.