Changing the concentration of reactants and products in a reversible chemical reaction at equilibrium affects the rate of the reaction according to Le Chatelier's Principle. This principle states that if a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the system will adjust itself to counteract the change and restore a new equilibrium.When the concentration of reactants is increased, the system will shift towards the products to counteract the change, thus increasing the rate of the forward reaction. This will result in the formation of more products until a new equilibrium is established.On the other hand, if the concentration of products is increased, the system will shift towards the reactants to counteract the change, thus increasing the rate of the reverse reaction. This will result in the formation of more reactants until a new equilibrium is established.Similarly, if the concentration of reactants is decreased, the system will shift towards the reactants to counteract the change, thus increasing the rate of the reverse reaction. This will result in the formation of fewer products until a new equilibrium is established.Lastly, if the concentration of products is decreased, the system will shift towards the products to counteract the change, thus increasing the rate of the forward reaction. This will result in the formation of fewer reactants until a new equilibrium is established.In summary, changing the concentration of reactants and products in a reversible chemical reaction at equilibrium affects the rate of the reaction by shifting the equilibrium position to counteract the change, either favoring the forward or reverse reaction until a new equilibrium is established.