The reaction between sodium thiosulfate Na2S2O3 and hydrochloric acid HCl is a well-known reaction in chemistry, often used to study reaction rates. The reaction produces a precipitate of sulfur S , which causes the solution to become cloudy:Na2S2O3 aq + 2 HCl aq 2 NaCl aq + SO2 g + S s + H2O l In this reaction, light intensity does not have a significant effect on the rate of the reaction. The reaction rate is primarily influenced by factors such as concentration, temperature, and the presence of catalysts. Light intensity may have an effect on reactions that involve photochemical processes, where light energy is absorbed by molecules and causes the reaction to occur. However, the reaction between sodium thiosulfate and hydrochloric acid is not a photochemical reaction, so light intensity does not play a significant role in the reaction rate.