Understanding the Law of Conservation of Mass

About a hundred years ago, Albert Einstein posited a brilliant deduction based on his theory of special relativity. One facet of Einstein’s theory suggested that matter and energy were related and he developed his famous E=mc2 formula to demonstrate this relationship. He further posited that energy and matter were simply different phases of the same thing and could not therefore be destroyed, but only transformed.

Since Einstein dropped these pearls of wisdom on us, his theories of relativity have been proved to be a true reality and are today respected by all credible scientists. Furthermore, scientist have used Einstein’s theories to define certain general physical laws which seem to hold true under all conditions. One such law which in terms of physics relates directly to Einstein’s special relativity, is the Law of Conservation of Matter and Energy. In Chemistry, this law is more often referred to as the Law of Conservation of Mass. The law basically states:

“in an ordinary chemical change, the total mass (weight) of the reacting materials is equal to the total mass (weight) of the products of the reaction.”

This law is so fundamental to an understanding of chemistry, that it is one of the first concepts chemistry students are exposed to and must grasp an understanding of. In fact, this precept is so elementary that within a few days chemistry students take it for granted factoring it into chemical equations without even thinking about it. 

In chemistry, a chemical equation in a way is like an algebraic expression, where what is on one side of the equal sign must be numerically congruent (equal)  to what is on the other side of the equal sign. In chemistry however, the variables of the equation are elements and compounds which react to form other compounds. The reaction itself in a chemical equation is represented with a “—>” symbol instead of an “=” symbol but the meaning is in actuality the same. That is where the Law of Conservation of Mass comes into play and  the reaction symbol —> is actually representative of this law at work. It specifies, that the mass (as represented by the atomic weight)  of the reactants must be equal to the mass of the products of the equation. For example, the formula hydrogen + oxygen —> water or H2 + O —> H2O demonstrates that for given quantities of hydrogen and oxygen, and equal quantity of water will be the result of the reaction.

The Law of Conservation of Mass has become a precept that generations before, currently and yet to come can count on when pondering the universe and interactions of matter and energy within it. We no longer have to guess and formulate whimsical notions about chemical phenomena as more ancient humans did, as this and other scientific laws allow us to understand and know with certainty, the relationships between matter and energy.