Question

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. The scientist needs to determine how many grams of copper sulfide the reaction will produce. In 1–2 sentences, explain how to calculate the amount of copper sulfate this reaction will produce. Use the law of conservation of mass in the explanation

Answer 1

You didn't write the equation but it is
............2Cu + S ==> Cu2S
.............12.7...3.2 ------12.7 + 3.2 = 15.9
The law of consecration of mass says matter is not created or destroyed so you start with 15.9 g and must end with 15.9 g.

Answer 2

Thanks @DrBob222