A sealed bag contains 10 g of iron filings and 5 g of sulfur. After the iron and sulfur react completely to form iron(II) sulfide inside the sealed bag, what will be the total mass of the bag and its contents?

• A. 10 g
• B. 20 g
• C. 5 g
• D. 15 g

Answer: (D)

Verified step by step guidance

1. Identify the law of conservation of mass, which states that mass is neither created nor destroyed in a chemical reaction. This means the total mass before the reaction equals the total mass after the reaction.
2. Determine the total mass of the reactants before the reaction by adding the mass of iron filings and sulfur: \$10\ \text{g} + 5\ \text{g}$.
3. Recognize that the reaction forms iron(II) sulfide inside the sealed bag, so no mass is lost or gained from the system.
4. Conclude that the total mass of the bag and its contents after the reaction will be the same as the total mass of the reactants before the reaction.
5. Therefore, the total mass after the reaction is the sum calculated in step 2, which is the mass of iron plus the mass of sulfur.