# Equilibrium :. Why does a system at equilibrium try to undo the effect of external stress applied on it? [duplicate]

" Le Chatelier principle states that a system at equilibrium when subjected to external stress tries to undo the effect of that stress"

In short, why does system at equilibrium follow Le Chatelier principle?

## marked as duplicate by Mithoron, andselisk, A.K., airhuff, aventurinJan 1 at 14:01

For example, suppose that as a result of molecular motion, a small part, A, of a larger volume of a gas spontaneously increases by $$\Delta V$$. Thus the pressure decreases, $$\Delta p < 0$$, and so the net force on A exerted by the surroundings is in a direction that tends to restore equilibrium.