Le Chatelier's Principle, also known as the Equilibrium Law, states that when a system at equilibrium is subjected to an external stress, the system will adjust in such a way as to partially offset the stress and maintain equilibrium.
The three main types of external stresses that can affect a system at equilibrium are changes in temperature, pressure, and concentration. These stresses can cause the equilibrium to shift in either the forward or reverse direction.
According to Le Chatelier's Principle, an increase in temperature will favor the endothermic reaction (a reaction that absorbs heat), while a decrease in temperature will favor the exothermic reaction (a reaction that releases heat). This is because the system will try to offset the external stress by favoring the reaction that produces or absorbs heat.
In a gaseous system, an increase in pressure will favor the reaction that produces fewer moles of gas, while a decrease in pressure will favor the reaction that produces more moles of gas. This is because the system will try to reduce the pressure by shifting the equilibrium in the direction that produces fewer gas molecules.
If the concentration of one of the reactants or products is increased, the equilibrium will shift in the direction that uses up that substance. On the other hand, if the concentration of one of the reactants or products is decreased, the equilibrium will shift in the direction that produces more of that substance. This is because the system will try to restore the original ratio of reactants and products in order to maintain equilibrium.