Antoine Lavoisier

Law of Conservation of Matter (Antoine Lavoisier)

The first breakthrough in the study of chemical reactions resulted from the work of the French chemist Antoine Lavoisier between 1772 and 1794. Lavoisier found that mass is conserved in a chemical reaction. The total mass of the products of a chemical reaction is always the same as the total mass of the starting materials consumed in the reaction. His results led to one of the fundamental laws of chemical behavior: the law of conservation of matter, which states that matter is conserved in a chemical reaction.

We now understand why matter is conserved -- atoms are neither created nor destroyed in a chemical reaction. Hydrogen atoms in a H₂ molecule can combine with oxygen atoms in an O₂ molecule to form H₂O, for example. But the number of hydrogen and oxygen atoms before and after the reaction is the same. The total mass of the products of a reaction therefore must be the same as the total mass of the reactants.

Origins of Stoichiometry (Antoine Lavoisier)

In his famous textbook, Trait lmentaire de Chimie, which was published in 1789, Lavoisier reported that water was roughly 85% oxygen and 15% hydrogen by weight. Water therefore seemed to contain 5.6 times more oxygen by weight than hydrogen.

The Process of Discovery:  The Elements (Antoine Lavoisier)

In 1661, when Boyle defined an element as a substance that can't be decomposed into a simpler substance by a chemical reaction, only 13 elements were known: antimony, arsenic, bismuth, carbon, copper, gold, iron, lead, mercury, silver, sulfur, tin, and zinc. By the end of the eighteenth century, when Lavoisier published a list of elements, another 11 had been discovered: chlorine, cobalt, hydrogen, manganese, molybdenum, nickel, nitrogen, oxygen, phosphorus, platinum, and tungsten. Since that time, a new element has been discovered on the average of every two and one-half years (see Figure 7.1.)