Dynamic equilibrium and le chatelier's principle

• What is happening in an equilibrium system?

  The rate of the forward reaction is equal to the rate of the reverse reaction.

  the concentration of reactants and products do not change
• What does dynamic mean in terms of equilibrium?

  At equilibrium both the forward and reverse reactions are taking place. As fast as the reactants are becoming products the products are reacting to become reactants. Therefore in an equilibrium system the concentrations of the reactants and products remain unchanged even though both reactions are still taking place.