2cu + s +cu2s
copper (cu) reacts with sulfur (s) to form copper sulfide as shown in the equation. A scientist adds 12.7 grams of Cu to 3.2 grams of S to start the reaction. in this reaction, all of the copper and all of the sulfur react. before running the experiment, the scientist expect the product of the reaction will be a total of 15.9 grams of copper sulfide (Cu2S). in 1 sentence explain how the law that the scientist use to predict that the product of the reaction would be 15.9 grams of copper sulfide