Copper sulfide is formed when copper and sulfur are heated together. In this reaction, 132 g of copper reacts with 53 g of sulfur. After the reaction is complete, 9 g of sulfur remains unreacted. What is the mass of copper sulfide formed?

Answer 1

This is a limiting reagent (LR) problem but they tell you that you have some S left over which means the LR is Cu.
2Cu + S ==> Cu2S
Follow the HgO problem to find mols Cu used up (all of it) and mols Cu2S formed (Note: the 9 g S unused is not use OTHER than so that you know Cu is the limiting reagent.)

Answer 2

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.