The rate of the reaction between hydrochloric acid HCl and magnesium Mg can be affected by the change in pH. The pH is a measure of the concentration of hydrogen ions H+ in a solution, and in the case of hydrochloric acid, it is directly related to the concentration of HCl.The reaction between HCl and Mg can be represented by the following balanced chemical equation:Mg s + 2HCl aq MgCl2 aq + H2 g As the pH decreases i.e., the concentration of H+ ions increases , the concentration of HCl in the solution also increases. This results in a higher frequency of collisions between the HCl and Mg particles, which in turn increases the rate of the reaction.Conversely, as the pH increases i.e., the concentration of H+ ions decreases , the concentration of HCl in the solution decreases. This leads to a lower frequency of collisions between the HCl and Mg particles, resulting in a slower rate of reaction.In summary, the change in pH affects the rate of the reaction between hydrochloric acid and magnesium by altering the concentration of HCl in the solution. A lower pH higher H+ ion concentration will increase the rate of the reaction, while a higher pH lower H+ ion concentration will decrease the rate of the reaction.