Dynamic equilibrium - effect of adding inert gas Well consider the reaction $A + B ⇌ C$
Adding inert gas to a container where this reaction is taking place will increase the pressure of the system. In accordance with Le Chatelier's Principle, the equilibrium should shift in the direction which opposes this change in pressure, i.e. in the direction where fewer number of molecules are created. In this specific reaction, it happens to be in the forward reaction. However, I have been taught that adding an inert gas at constant volume has no effect on the equilibrium. Why is this?
At constant temperature, only changes to the concentration (technically activity) of a reactant or product, shift the equilibrium.  

Adding inert gas does not change the concentration of any reactant or product, so it does not affect equilibrium.