Which of the following is always conserved in every chemical reaction according to the Law of Conservation of Mass?

• A. Volume
• B. Energy
• C. Mass
• D. Number of molecules

Answer: (C)

Verified step by step guidance

1. Understand the Law of Conservation of Mass, which states that mass cannot be created or destroyed in a chemical reaction; it remains constant throughout the process.
2. Recognize that volume can change during a reaction because gases can expand or contract, and liquids or solids can change state, so volume is not always conserved.
3. Consider energy: while energy is conserved overall (according to the Law of Conservation of Energy), it can change forms (e.g., heat, light), so energy conservation is a separate principle from mass conservation.
4. Note that the number of molecules can change because molecules can break apart or combine to form new molecules during a reaction, so the number of molecules is not necessarily conserved.
5. Conclude that the quantity always conserved in every chemical reaction, according to the Law of Conservation of Mass, is the total mass of the reactants and products.