What is Lavoisier’s law?

Lavoisier’s law

By developing more precise ideas about elements , compounds, and mixtures , scientists began to investigate how and why substances reacted with each other. The French chemist A. Lavoisier was the one who laid the foundations for the scientific investigation of matter by describing that substances react according to certain laws. These laws are called laws of chemical combination .

Lavoisier's law

What is Lavoisier’s law?

The law of Lavoisier is a law that tells us that in all reactions chemicals that are made, the mass of the reaction components are preserved , never destroys nor creates new matter, the only thing that happens is that reorganizes .

  • What is Lavoisier’s law?
  • History
  • Who proposed it
  • Statement of Lavoisier’s law
  • Formula
  • Experiments
  • Applications
  • Importance of Lavoisier’s law
  • Examples

What is Lavoisier’s law?

Lavoisier’s law consists of a statement that tells us that in every chemical reaction , the mass is conserved , in other words it tells us that the total mass of the reactants is equal to the total mass of the products . In short, it explains that matter is not created or destroyed during a chemical process, but only rearranges itself .

The law is one of the pillars of the birth of the chemical equation along with the modern nomenclature that chemical compounds have . It is named after Antoine Laurent Lavoisier , a French chemist whose work was so important that it still stands as the basis of modern chemistry.


Lavoisier is considered to be the forerunner of modern chemistry , and he was the one who made one of the most important discoveries in this science, the Law of Conservation of Mass . During the 18th century, little attention was paid to the quantitative aspect of science. Substances were mixed, their powders and gases were observed and described, but they were not measured. Then Lavoisier appeared who thought that measurement was the most important part and that this was the basis for chemical experiments .

Lavoisier was born in Paris in 1743, had an excellent education, received a law degree , then studied Astronomy , Natural History , and Chemistry. He worked for years in science and technology and discovered the secret of what the alchemists called the “transformation of water into land” and that for them was clear proof of the transmutation of elements .

He established that air is a mixture of 27% oxygen and 79% nitrogen . He specified the notion of pure substance , adopting Boyle’s concept of ” element “. He used the Principle of Conservation of Matter and made the first calorimetric measurements . He demonstrated the presence of oxygen in bases and acids and collaborated in the elaboration of a new chemical nomenclature , very similar to the current one, in which the names of the substances reflect their chemical composition.

Who proposed it

Lavoisier’s law was proposed by Antoine-Laurent de Lavoisier (1743-1794) who was a renowned French economist, chemist, and biologist, an important figure in the chemical revolution of the 18th century.

Statement of Lavoisier’s law

The statement of Lavoisier’s law can be given in three different ways which are:

  • The matter is neither created nor destroyed , only transformed .
  • In a chemical reaction the sum of the mass of the reactants is equal to the sum of the mass of the products.
  • In a chemical reaction the atoms do not disappear , they are simply arranged in another way.


Lavoisier’s law formula tells us that the mass of the reactants = the mass of the products.


Add 50 ml of vinegar to an Erlenmeyer flask and weigh on the balance. Then add two teaspoons of baking soda to a glass to record its weight accurately, and then add the baking soda to the vinegar . Observe during the reaction what happens and if the Erlenmeyer flask increases or decreases its temperature. When the reaction ends, the Erlenmeyer flask is weighed to obtain the weight of the products .


Some of the most important applications of the law are the following:

  • Know the mass of reagents that are needed to obtain a certain amount of product in a chemical reaction
  • Performing stoichiometric calculations .
  • Pillar of chemical reactions
  • The pharmaceutical industry builds on it

Importance of Lavoisier’s law

Thanks to its law is known today that the theory of the phlogiston on combustion was false, that matter can get to change and create new substances, but does not have the ability to come out of nowhere or disappear . Thanks to his law of conservation of matter , the foundations of current nomenclature and chemistry were created , and measuring compounds became of vital importance for research in the area of ​​chemistry.


Some everyday situations where we can observe Lavoisier’s law are the following:

  • In the different chemical combustion reactions  , such as when burning a certain product and leaving a little of the mass in ashes and the rest is transformed into gases.
  • The boiling that is generated when it is heated for example 100 grams of water in a liquid state that when it is heated and boils leaves as a result 100 grams of steam after a long time.
  • When preparing a lemonade in which 100 grams of sugar are placed, 500 grams of water and 50 grams of lemon juice, this does not give a total of 650 grams of the total mixture.
  • When a car is put 40 Kilograms of fuel , after having consumed all the fuel, the car will weigh 40 Kilograms less, but in the environment there are 0 Kilograms more of gases that have arisen as a result of combustion .
  • In the digestive process , when a person eats, the body absorbs what it needs to transform it into energy and expels what it does not need in the form of urine and feces .

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