The physical universe is governed by immutable laws that dictate how matter and energy interact. These principles provide a reliable framework for understanding all observable phenomena, from chemical reactions to stellar events. Science seeks to describe these inherent rules, which ensure that in any physical process, certain quantifiable properties remain constant.
The Law of Conservation of Mass
The specific law stating that matter cannot be destroyed is the Law of Conservation of Mass, also known as the Law of Conservation of Matter. This principle asserts that for any system closed to all transfers of matter, the system’s mass must remain constant over time. Although matter may change form, its total quantity remains the same, as atoms are simply rearranged to form new substances.
This law means that in a chemical reaction, the total mass of the starting materials (reactants) is precisely equal to the total mass of the final substances (products). The formulation of this concept was a major step in the development of modern chemistry, moving the field away from earlier, less quantitative theories.
Historical credit for formalizing this law is given to the French chemist Antoine Lavoisier, who conducted meticulous experiments in the late 18th century. By performing reactions inside sealed vessels, he demonstrated quantitatively that the total mass before and after combustion remained unchanged. Lavoisier’s work established that combustion was a chemical reaction involving the combination of a substance with oxygen.
Observing Mass Conservation
The Law of Conservation of Mass is best observed in a closed system, an environment where neither matter nor energy can enter or escape. When a reaction occurs in a sealed container, gaseous products are trapped, ensuring their mass is accounted for in the final measurement. Reactions performed in an open vessel might appear to lose mass if a gas is produced and escapes into the surrounding air.
This principle is fundamental to balancing chemical equations, a method used to represent chemical reactions. A balanced equation must show the same number and type of atoms on both the reactant and product sides. This mathematical balancing reflects the physical reality that atoms are merely reconfigured into new molecular structures during the reaction.
A common example illustrating this concept is the burning of wood. The resulting ash weighs less than the original log because the solid matter converts into gases, primarily carbon dioxide and water vapor, which escape the open system. If the entire combustion process were contained within a sealed system, the mass of the wood and the consumed oxygen would exactly equal the mass of the ash and the gases produced.
The Relationship Between Mass and Energy
The classical Law of Conservation of Mass is accurate for everyday chemical changes, but high-energy phenomena, such as nuclear reactions, require a deeper understanding. In the early 20th century, Albert Einstein introduced Mass-Energy Equivalence, summarized by \(E=mc^2\). This equation reveals that mass and energy are fundamentally interchangeable and are different manifestations of the same underlying physical entity.
The truly universal governing principle is the Law of Conservation of Mass-Energy, which states that the total combined amount of mass and energy in a closed system remains constant. This refinement is necessary because in processes like nuclear fusion or fission, a measurable amount of mass is converted into energy, or vice versa. The system appears to lose mass, but that mass has transformed into the kinetic energy of the resulting particles and radiation.
The change in mass during standard chemical reactions is so minuscule that it is essentially undetectable, making the classical Law of Conservation of Mass a robust and practical rule for chemistry. Conversely, in nuclear reactions, the conversion of mass to energy is a significant percentage of the initial mass, requiring the comprehensive Law of Conservation of Mass-Energy to accurately account for all components.