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Equilibrium and increasing the yield of PCl5 from PCl3 and Cl2

Submitted by brandi11 on Tue, 07/12/2011 - 11:01

Consider the equilibrium of the equation:  PCl3 (g) + Cl2 (g) <-----> PCl5 (g)   Delta H rxn= -111kJ

As a head chemist at a chemical plant, you are in charge of the amount of PCl5 that is produced daily. List two ways to produce more PCl5 (one way involving changing temperature an one involving changing the concentration).


LeChatlier's Principle says that increasing a stress on a system at equilibrium will cause the system to shift in such a way as to alleviate the stress.

Since delta H is negative the reaction is exothermic or produces heat.  If the manager lowers the the temperature in the reaction vessel it will cause the reaction to shift toward the products thus producing more heat (replacing the stress of removing heat by lowering the temperature).

 

Increasing the pressure of the reactants will also cause the reaction to shift toward the products.  The stress in this case would be the increased concentrations of the reactants which is reduced when the reactants are used up to make more product.