Chapter 13, Problem 8ALQ

Le Châtelier’s principle is stated (Section 12-7) as follows: “If a change is imposed on a system at equilibrium, the position of the equilibrium will shift in a direction that tends to reduce that change.” The system ${\text{N}}_2\left(g\right)+3{\text{H}}_2\left(g\right)\rightleftharpoons 2{\text{NH}}_3\left(g\right)$ is used as an example in which the addition of nitrogen gas at equilibrium results in a decrease in H₂ concentration and an increase in NH₃, concentration. In the experiment the volume is assumed to be constant. On the other hand, if N₂ is added to the reaction system in a container with a piston so that the pressure can be held constant, the amount o f NH₃ actually could decrease, and the concentration of H₂ would increase as equilibrium is reestablished. Explain how this can happen. Also, if you consider this same system at equilibrium, the addition of an inert gas. holding the pressure constant, does affect the equilibrium position. Explain why the addition of an inert gas to this system in a rigid container does not affect the equilibrium position.