Question

The dissociation of PCl5(g) to PCl3(g) and Cl2(g) is an endothermic reaction.  

PCl₅(g)        PCl₃(g)     +     Cl₂(g)

       What is the effect on the position of equilibrium of each of the following changes?

a)    Compressing the gaseous mixture                           _________________________________

b)    Decreasing the temperature                                   _________________________________             

c)    Adding Cl2(g) to the equilibrium mixture                __________________________________

d)    Removing PCl5 (g) from the equilibrium mixture   __________________________________

Answer 1

The dissociation of PCl5(g) to PCl3(g) and Cl2(g) is an endothermic reaction, i.e., heat is supplied to the system to complete.

PCI₅(g) --> PCI₃(g) + CI₂(g)

The Le-Chatliers principle will explain the effect on the equilibrium.

It states that when equilibrium is disturbed by any factor, temperature pressure, concentration, etc., the system tries to maintain the same by counteracting that parameter as long as it is possible.

A. Compressing the gas mixture

When the given system is compressed, means increase the pressure, the system will try to decrease the pressure according to the Le-Chatliers princ;iple hence the equilibrium will shift to, left favoring the formation of reactants back because the on reactant, side only one mole of partial pressure is there while in product side two moles. Therefore equilibrium shifts to the left.

B. Decreasing the temperature.

Since the reaction is endothermic, heat is supplied to the system to carry out the reaction; hence according to the principle, decreasing the temperature will again favor the reactant's formation. Optimum temperature is maintained must carry out the reaction.

C. Addition of chlorine

This will again result in the formation of reactant. By increasing the number of moles of the chlorine, the system will try to decrease chlorine concentration; hence more PCl5 will be formed.

D. Removing PCl5 (g).

By removing this from the equilibrium, the system will increase according to the Le Chatliers principle.