The effect of changing the concentration of reactants on the rate of a chemical reaction can be explained using the collision theory. According to this theory, the rate of a reaction depends on the frequency of effective collisions between reactant particles. When the concentration of reactants increases, the number of particles per unit volume also increases, leading to a higher probability of effective collisions and thus an increased reaction rate.As for the sustainability of a chemical reaction, it depends on the availability of reactants. If the concentration of reactants is too low, the reaction may not proceed at a significant rate or may not be sustainable over time. On the other hand, if the concentration is too high, it may lead to side reactions or the formation of unwanted products.To demonstrate the effect of concentration on reaction rate experimentally, one can use the reaction between sodium thiosulfate Na2S2O3 and hydrochloric acid HCl as an example. This reaction produces a precipitate of sulfur S , which makes the solution cloudy:Na2S2O3 aq + 2HCl aq 2NaCl aq + SO2 g + S s + H2O l The rate of this reaction can be measured by monitoring the time it takes for the solution to become cloudy i.e., when a certain amount of sulfur has precipitated . By performing this reaction with different initial concentrations of sodium thiosulfate and/or hydrochloric acid, one can observe the effect of concentration on the reaction rate.To carry out the experiment:1. Prepare a series of sodium thiosulfate solutions with different concentrations e.g., 0.1 M, 0.2 M, 0.3 M, etc. .2. Keep the concentration of hydrochloric acid constant e.g., 1 M .3. Mix equal volumes of sodium thiosulfate and hydrochloric acid solutions in a conical flask placed on a white background with a black cross.4. Start a timer as soon as the solutions are mixed.5. Observe the time it takes for the black cross to disappear due to the formation of sulfur precipitate, which indicates the reaction rate.6. Record the time for each trial and calculate the reaction rate 1/time .7. Plot a graph of reaction rate vs. concentration of sodium thiosulfate.The results should show that the reaction rate increases with increasing concentration of sodium thiosulfate, demonstrating the effect of concentration on the rate and sustainability of the reaction.