Encyclopedia of Science | Conservation Laws

• Conservation of mass and energy
• Words to Know
• Other conservation laws

Conservation laws are scientific statements that describe the amount of some quantity before and after a physical or chemical change.

Conservation of mass and energy

One of the first conservation laws to be discovered was the conservation of mass (or matter). Suppose that you combine a very accurately weighed amount of iron and sulfur with each other. The product of that reaction is a compound known as iron(II) sulfide. If you also weigh very accurately the amount of iron(II) sulfide formed in that reaction, you will discover a simple relationship: The weight of the beginning materials (iron plus sulfur) is exactly equal to the weight of the product or products of the reaction...