The law of definite proportions, also known as the law of constant composition, is a fundamental principle in chemistry that describes the consistent mass ratio of elements in a chemical compound. It states that a compound is composed of elements combined in definite proportions by mass, regardless of the sample size or source of the compound.
According to this law, the relative masses of the elements in a compound are fixed and constant. For example, water (H2O) is always composed of two hydrogen atoms and one oxygen atom, resulting in a fixed mass ratio of 2:16. Regardless of the quantity of water, this ratio remains constant.
The law of definite proportions is crucial in determining the identity of compounds and their chemical formulas. It allows scientists to predict the precise elements and their quantities within a given compound.
The concept was first formulated and demonstrated by French chemist Joseph-Louis Proust in the late 18th century. Proust conducted numerous experiments, consistently finding that compounds had a fixed ratio of elements by mass. His findings ultimately led to the development of the law of definite proportions, which revolutionized the understanding of chemical reactions and compound formation.
Today, this law remains a cornerstone of chemical research and analysis, serving as an essential principle in stoichiometry, chemical equations, and the determination of molecular formulas.
