Recall that a chemical reaction reaches an equilibrium when the rates of forward and reverse reactions are equal. At that point, the concentrations of reactants and products do not change.
Le Chatelier's principle describes what happens to a system when something momentarily takes it away from equilibrium. If more reactant is added, the equation will shift to the right in order to make more product. If the temperature is decreased, the reaction will shift to the right to create more heat if it is exothermic (which will increase the product), and to the left if it is endothermic (which will decrease the products). <span> If the pressure is decreased, it will shift in the direction where there are more moles of gas present, because it can now take up more space.</span>
