Final answer:
A change in the concentration of a reactant or product causes a chemical system at equilibrium to shift and counteract the introduced stress, as per Le Chatelier's Principle, in order to re-establish a new equilibrium.
Step-by-step explanation:
Understanding Chemical Equilibrium and Le Chatelier's Principle
When a chemical equilibrium is disturbed by changing the concentration of either a reactant or a product, it results in a stress to the system. According to Le Chatelier's Principle, the reaction will shift to counteract this stress and establish a new equilibrium. For example, if the concentration of a reactant increases, the rate of the forward reaction will increase to consume the added reactant, subsequently producing more product. Conversely, if a reactant is removed or a product is added, the rate of the reverse reaction will increase to use up the excess product and generate more reactants, thus restoring equilibrium.
Reaction rates are affected by both concentration and temperature. In the context of equilibrium, a change in concentration leads to a change in reaction rates. An increase in reactant concentration causes the system to produce more products (shift right), while an increase in product concentration results in more reactant formation (shift left). In both scenarios, the equilibrium will shift in such a way to reduce the stress and re-establish the balance between the forward and reverse reactions.