Which law states that matter cannot be created or destroyed during a chemical reaction?

The law that states matter cannot be created or destroyed during a chemical reaction is the Law of Conservation of Mass. This principle asserts that the total mass of reactants in a chemical reaction is equal to the total mass of the products. This means that all atoms present at the start of the reaction are accounted for in the final products, just rearranged into different molecules rather than being lost or gained.

In contrast to this law, the Law of Definite Proportions relates to the fixed ratios of elements that compose a given compound, indicating that a chemical compound always contains the same proportion of elements, regardless of the amount of the compound. The Laws of Thermodynamics pertain to energy conservation and transfer within physical systems, but do not directly address the conservation of mass or matter. Lastly, the Law of Conservation of Energy focuses on the principle that energy cannot be created or destroyed, only transformed from one form to another, which, while similar in nature to the conservation of mass, addresses energy rather than matter.