A certain amount of PCl3 Cl2 and PCl5 is mixed in a 200L fla

A certain amount of PCl3, Cl2 and PCl5 is mixed in a 2.00L flask for the following reaction:

PCl3(g) + Cl2(g) PCl5(g) H = 111kJ. At equilibrium, [PCl3] = 0.200M, [Cl2] = 0.125M, [PCl5] = 0.600 M.

A) If 0.150mol more gaseous Cl2 is added to the above system, what is the concentration of PCl5 when the system reach new equilibrium?

B) Predict the yield change of PCl5 by increasing the container volume? Explain your answer fully.

C) Predict the yield change of PCl5 by increasing temperature? Explain your answer fully.

Solution

for the reaction , PCl3(g)+Cl2(g) <---->PCl5(g)

K= [PCl5]/ [PCl3][Cl2] = 0.6/(0.125*0.2)= 24

when 0.15 moles of Cl2 is added, the new concentration of Cl2= 0.125+0.15/2=0.2

The reaction coefficient Q= 0.6/(0.2*0.2)= 15<K, so the reaction proceeds so as to produts side ( i.e formation of more PCl5)

let x= drop in concentration of PCl3 to reach equilibrium

at equilibrium, [PCl3]= 0.2-x and [Cl2]=0.2-x and [PCl5]=0.6+x

K= (0.6+x)/(0.2-x)²= 24, when solved for x using excel, x=0.0371

[PCl3]=0.2-0.0371=0.1629M, [Cl2]=0.2-0.0371= 0.1629M, [PCl5]=0.6+0.0371= 0.6371M

2. When volume is increased, at constant temperature and pressure no of moles is proportional to volume

so increase in volume increases no of moles, so there is an increase in no of moles, so as per Lechatlier principle,

the reaction proceeds in a direction where there is a decrease in no of moles. So the reaction proceeds towards formation of PCl5.

The reaction is exothermic as indicated by change in enthalpy being -ve. So when temperature is increased as per Lechtlier principle, the reaction proceeds in a direction so as to compensate the effect of increased temperature. So the reaction proceeds in the endothermic direction. So backward reaction is favored. So more PCl3 and Cl2 are formed,