Matter cannot be created or destroyed; the mass at the start must equal the mass at the end. Which law is this?

Matter cannot be created or destroyed; the mass at the start must equal the mass at the end. Which law is this?

• A. Law of Conservation of Energy
• B. Law of Conservation of Mass
• C. Law of Thermodynamics
• D. Law of Motion

Answer: (B)

Matter cannot be created or destroyed; the mass at the start must equal the mass at the end. This is the Law of Conservation of Mass. In any chemical reaction or physical change that occurs in a closed system, the atoms present before the change are the same atoms present after, just rearranged. The total mass remains the same because no atoms are gained or lost. For example, when wood burns in a sealed container, the mass of the ashes, gases, and remaining char plus the oxygen that reacted is equal to the mass of the original wood and oxygen entering the container. That balance is why mass is conserved. The other options describe different ideas: the Law of Conservation of Energy says energy itself is conserved, not mass, and though energy and mass are related by relativity, everyday chemistry treats mass as conserved. The Law of Thermodynamics focuses on energy transfer, heat flow, and the direction of processes, not mass alone. The Law of Motion deals with forces and how objects move.

Matter cannot be created or destroyed; the mass at the start must equal the mass at the end. This is the Law of Conservation of Mass. In any chemical reaction or physical change that occurs in a closed system, the atoms present before the change are the same atoms present after, just rearranged. The total mass remains the same because no atoms are gained or lost.

For example, when wood burns in a sealed container, the mass of the ashes, gases, and remaining char plus the oxygen that reacted is equal to the mass of the original wood and oxygen entering the container. That balance is why mass is conserved.

The other options describe different ideas: the Law of Conservation of Energy says energy itself is conserved, not mass, and though energy and mass are related by relativity, everyday chemistry treats mass as conserved. The Law of Thermodynamics focuses on energy transfer, heat flow, and the direction of processes, not mass alone. The Law of Motion deals with forces and how objects move.