Overview
This lecture explains the law of conservation of mass, highlighting that matter is neither created nor destroyed during a chemical reaction, as demonstrated by a methane combustion example.
Law of Conservation of Mass
- The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction.
- In a closed container, the total mass before and after a chemical reaction remains the same.
- Atoms are rearranged during a reaction, but their total mass stays constant.
Example: Methane Combustion Reaction
- If 16 g of methane reacts with 64 g of oxygen in a closed container, the total starting mass is 80 g.
- After combustion, the products are carbon dioxide and water vapor.
- If 44 g of carbon dioxide is produced, then the mass of water produced is 80 g - 44 g = 36 g.
- The reaction does not lose or gain mass; products' total mass equals reactants' total mass.
Key Terms & Definitions
- Law of Conservation of Mass — Matter cannot be created or destroyed in a chemical reaction; total mass remains constant in a closed system.
- Reactants — Substances present at the start of a chemical reaction (e.g., methane and oxygen).
- Products — Substances formed as a result of a chemical reaction (e.g., carbon dioxide and water vapor).
- Closed System — A physical system that does not allow mass to enter or leave during a reaction.
Action Items / Next Steps
- Practice identifying reactants and products in given chemical reactions.
- Solve additional mass conservation problems using the law of conservation of mass.