Why is the law of conservation of mass still valid when a gas is produced in a reaction carried out in a closed container?

• A. Gases escape but their mass is negligible.
• B. Mass is not conserved in gases.
• C. Because the total mass of reactants equals total mass of products in a closed system.
• D. The law only applies to solids.

Answer: (C)

Mass is conserved in chemical reactions because atoms are rearranged, not created or destroyed. In a closed container, nothing can enter or leave, so the total mass inside stays the same. When a gas is produced, it has mass too, so the mass of all reactants equals the mass of all products combined inside the container. The change in state to a gas doesn’t affect the total mass; it just changes how that mass is distributed among substances.