The physical world operates under certain fundamental rules that govern how everything interacts. Among the most important of these rules, particularly in chemistry and physics, is the Law of Conservation of Matter. This concept provides the foundation for understanding all physical and chemical processes that occur around us every day. It is a simple but powerful idea that establishes a baseline for all scientific measurements and observations.
Defining the Law of Conservation of Matter
The Law of Conservation of Matter states that matter can neither be created nor destroyed. The total quantity of matter in an isolated system remains constant, regardless of the changes matter undergoes. This means that in any physical or chemical change, the total mass of the materials before the change must equal the total mass of the materials after the change.
Matter refers to anything that has mass and takes up space, built from atoms and molecules. When a change occurs, these atoms are simply reorganized, like rearranging LEGO bricks into a new structure. No individual atom is lost, nor are any new atoms spontaneously generated during the process. This is why the law is sometimes also called the Law of Conservation of Mass. The total number and type of atoms involved remain precisely the same from start to finish.
Observing the Law in Action
The principle is best understood by looking at how matter behaves during transformations.
Physical Changes
In a physical change, such as melting ice, the water molecules (H₂O) simply move farther apart as the substance shifts from a solid to a liquid. If you weigh an ice cube and then weigh the resulting liquid water, the mass will be identical. The matter has only changed its state, as the number of H₂O molecules has not changed.
Chemical Changes
The law is also maintained during a chemical change, where new substances are formed. For instance, when wood burns, it may seem like matter is being destroyed because the resulting ash has a much lower mass than the original log. However, the wood combines with oxygen from the air and rearranges its atoms to form gases, specifically carbon dioxide and water vapor, which escape into the atmosphere.
If the burning were to take place in a sealed, or closed, container that prevented the gases from escaping, the total mass of the wood, plus the oxygen, plus the ash and gases would exactly equal the starting mass. This concept of a “closed system” is important for observation because it ensures that nothing can escape or enter the reaction. In a simple chemical reaction, like mixing baking soda and vinegar, the atoms of the starting materials (reactants) merely reform the bonds to create new products. By accounting for the mass of all products, including the invisible gases, scientists consistently confirm that matter is conserved.
Matter and Energy: Clarifying the Relationship
For nearly all chemical and physical changes encountered in daily life, the Law of Conservation of Matter is perfectly accurate and sufficient. However, the discovery of mass-energy equivalence by Albert Einstein introduced a slight modification to this classical law. Einstein’s famous equation, E=mc², shows that mass and energy are fundamentally interchangeable and are different forms of a single quantity called mass-energy.
In extreme events, such as nuclear reactions like fusion or fission, a tiny, measurable amount of mass is converted into a huge amount of energy. While this means mass itself is not strictly conserved in a nuclear process, the more comprehensive principle, the Law of Conservation of Mass-Energy, holds true. This broader law states that the total amount of mass and energy combined in the universe remains constant. For the purposes of chemistry and everyday science, the mass change from energy loss or gain is so incredibly small it is undetectable and can be ignored.