The reaction between magnesium Mg and hydrochloric acid HCl can be represented by the following balanced chemical equation:Mg s + 2 HCl aq MgCl aq + H g When the concentration of reactants is varied in a chemical reaction, the rate of the reaction is generally affected. In the case of the reaction between magnesium and hydrochloric acid, altering the amount of magnesium used will change the stoichiometry of the reaction, which in turn affects the rate of the reaction.If the amount of magnesium is increased while keeping the concentration of hydrochloric acid constant, the rate of the reaction will initially increase. This is because there are more magnesium atoms available to react with the hydrochloric acid molecules, leading to more frequent collisions between the reactant particles and a faster rate of reaction.However, as the reaction progresses, the concentration of hydrochloric acid will decrease due to its consumption in the reaction. As a result, the rate of the reaction will eventually decrease, as there will be fewer hydrochloric acid molecules available to react with the magnesium atoms. This effect is in accordance with the collision theory, which states that the rate of a reaction depends on the frequency of effective collisions between reactant particles.In summary, varying the concentration of reactants in the reaction between magnesium and hydrochloric acid by altering the amount of magnesium used will affect the rate of the reaction. Initially, increasing the amount of magnesium will lead to a faster reaction rate, but as the concentration of hydrochloric acid decreases over time, the rate of the reaction will eventually decrease.