The initial concentration of the reactants plays a significant role in determining the reaction rate in the chemical reaction between hydrochloric acid HCl and magnesium Mg . The reaction can be represented by the following balanced equation:Mg s + 2HCl aq MgCl2 aq + H2 g According to the collision theory, the reaction rate depends on the frequency of effective collisions between the reacting particles. When the initial concentration of the reactants is higher, there are more particles present in the same volume, which increases the probability of collisions between the particles. Consequently, the reaction rate increases.In the case of the reaction between hydrochloric acid and magnesium, increasing the concentration of HCl will result in a faster reaction rate. This is because there will be more HCl molecules available to collide with the magnesium atoms, leading to a quicker formation of magnesium chloride MgCl2 and hydrogen gas H2 .It is important to note that the concentration of magnesium does not have a direct impact on the reaction rate, as it is a solid reactant. However, increasing the surface area of magnesium can also increase the reaction rate, as it provides more opportunities for collisions between magnesium atoms and HCl molecules.In summary, the initial concentration of the reactants affects the reaction rate in the chemical reaction between hydrochloric acid and magnesium by increasing the frequency of effective collisions between the reacting particles. A higher concentration of HCl will lead to a faster reaction rate, while increasing the surface area of magnesium can also contribute to an increased reaction rate.