What is the effect of adding a reactant to a system at equilibrium?

Adding a reactant to a system at equilibrium results in an increase in the concentration of that reactant. According to Le Chatelier's principle, if a system at equilibrium experiences a change in concentration, temperature, or pressure, the system will adjust to counteract that change and establish a new equilibrium. In this case, the increase in reactants drives the reaction forward to use up some of the added reactants, shifting the equilibrium position toward the products.

This shift continues until a new equilibrium is reached where the rates of the forward and reverse reactions are equal again, but the concentrations of the products will be higher than before. Thus, the system favors the formation of products in response to the added reactants.