What is the law of definite proportions?

The law of definite proportions, also known as the law of constant composition, states that a chemical compound always contains the same elements in the same proportion by mass regardless of the source of the compound or how it was prepared. This means that a compound will always have a fixed ratio of the elements that make it up.

For example, water (H2O) will always consist of two hydrogen atoms for every one oxygen atom, and carbon dioxide (CO2) will always have one carbon atom for every two oxygen atoms.

The law of definite proportions was first formulated by French chemist Joseph Proust in the late 18th century. It is a fundamental principle in chemistry that helps to explain the behavior of chemical compounds and reactions.

The law of definite proportions is a key concept in stoichiometry, the branch of chemistry that deals with the quantitative relationships between reactants and products in chemical reactions. By understanding and applying this law, chemists can predict the outcomes of reactions and determine the composition of substances with a high degree of accuracy.