What effect do the following changes have on the position of equilibrium (which way does the equilibrium shift) for the reversible endothermic reaction? PCL5+ heat <-> PCL3(g)+ CL2(g)

Question

A) removal of PCL3, as it is formed
B)addition of CL2
C) decrease in pressure
D) putting in an ice bath

Answer 1

PCl5(g) + heat <-> PCl3(g)+ Cl2(g)
A) removal of PCl3, as it is formed
B)addition of Cl2
C) decrease in pressure
D) putting in an ice bath
What does Le Chatelier's Principle say. In long words it is this.
When a chemical system in equilibrium is subjected to a stress it will shift in such a way so as to relieve the stress. My students never got that so we came up with a simpler one. Here it is. A system in equilibrium will try to undo what we do to it.
For A. If we remove PCl3 the system will shift to form more of it. Simple. Shifts to the right; therefore, the amount of Cl2 @ equilibrium will be higher and the amount of PCl5 will be smaller.
C. If we decrease pressure the system will shift to lessen the pressure. How can it do that? By decreasing the number of moles of gas. So it will shift to the left BECAUSE there are fewer moles on the left (1 mol gas) than the right(2 mols gas). So the amount of PCl3 and Cl2 will decrease at equilibrium because there are fewer moles of gas present that way.
I've never understood why students get confused over this. In my opinion it is the simplest fundamental principle in chemistry. I'll leave B and D for you to do. I shall be happy to check your answers.