Altering the concentrations of reactants and products at equilibrium affects the rate of the forward and reverse reactions in a chemical system according to Le Chatelier's principle. This principle states that if a change is made to a system at equilibrium, the system will adjust itself to counteract the change and re-establish equilibrium.When the concentration of reactants is increased, the system will respond by shifting the equilibrium position to favor the forward reaction. This will increase the rate of the forward reaction, consuming the added reactants and forming more products until a new equilibrium is established. Conversely, if the concentration of reactants is decreased, the system will shift the equilibrium position to favor the reverse reaction, decreasing the rate of the forward reaction and increasing the rate of the reverse reaction.Similarly, when the concentration of products is increased, the system will shift the equilibrium position to favor the reverse reaction. This will increase the rate of the reverse reaction, consuming the added products and forming more reactants until a new equilibrium is established. If the concentration of products is decreased, the system will shift the equilibrium position to favor the forward reaction, increasing the rate of the forward reaction and decreasing the rate of the reverse reaction.In summary, altering the concentrations of reactants and products at equilibrium affects the rate of the forward and reverse reactions in a chemical system by shifting the equilibrium position to counteract the change and re-establish equilibrium, according to Le Chatelier's principle.