The concentration of reactants plays a significant role in the reaction rate and sustainability of the reaction between hydrochloric acid HCl and sodium thiosulphate Na2S2O3 . This reaction can be represented by the following balanced chemical equation:2HCl aq + Na2S2O3 aq 2NaCl aq + H2O l + SO2 g + S s The reaction rate is directly proportional to the concentration of the reactants. According to the collision theory, increasing the concentration of reactants increases the number of particles in a given volume, which in turn increases the frequency of collisions between the reacting particles. As a result, the reaction rate increases.In the context of the reaction between HCl and Na2S2O3, if the concentration of either HCl or Na2S2O3 is increased, the reaction rate will increase as well. This can be observed experimentally by monitoring the formation of the sulfur precipitate S s , which causes the solution to become cloudy.The sustainability of the reaction refers to the ability of the reaction to continue until one of the reactants is completely consumed. In this case, the sustainability of the reaction depends on the stoichiometry of the reactants. If the reactants are present in their stoichiometric ratio 2 moles of HCl for every 1 mole of Na2S2O3 , the reaction will continue until both reactants are completely consumed.However, if one of the reactants is present in excess, the reaction will continue until the limiting reactant is consumed, and the excess reactant will remain in the solution. For example, if there is an excess of HCl, the reaction will stop once all the Na2S2O3 has reacted, leaving some unreacted HCl in the solution.In summary, the concentration of reactants affects the reaction rate and sustainability of the reaction between hydrochloric acid and sodium thiosulphate. Increasing the concentration of either reactant will increase the reaction rate, while the sustainability of the reaction depends on the stoichiometry of the reactants.