This law was drafted in 1774 by the French chemist Antoine Laurent Lavoisier. Lavoisier's experimental studies led him to conclude that in a chemical reaction, which takes place in a closed system, the sum of the reactant masses is equal to the sum of the product masses:
m (reagents) = m (products)
Thus, for example, when 2 grams of hydrogen react with 16 grams of oxygen, 18 grams of water is formed; When 12 grams of carbon react with 32 grams of oxygen, 44 grams of carbon dioxide is formed.
This law has even been incorporated into the "popular knowledge" and is often stated as:
"In nature nothing is created, nothing is lost, everything is transformed."
Law of Constant Proportions (Proust's Law)
This law was drafted in 1797 by chemist Joseph Louis Proust. He found that the masses of reactants and the masses of products that participate in a chemical reaction always follow a constant proportion. This ratio is characteristic of each reaction and independent of the amount of substances that are put to react. Thus, for the reaction between hydrogen and oxygen forming water, the following experimental values can be obtained:
- for each reaction, the mass of the product is equal to the mass of the reactants, which is in accordance with Lavoisier's law;
- The reactant and product masses participating in the reactions are different, but the oxygen mass / hydrogen mass, water mass / hydrogen mass and water mass / oxygen mass ratios are always constant.
m oxygen / m hydrogen
m water / m hydrogen
m water / oxygen
8/10 = 8
90/10 = 9
90/80 = 1,125
16/2 = 8
18/2 = 8
18/16 = 1,125
8/1 = 8
9/1 = 9
9/8 = 1,125
3,2/0,4 = 8
3,6/0,4 = 9
3,6/3,2 = 1,125
In the case of synthesis reactions, that is, those which originate a substance from its constituent elements, the statement of Proust's law may be as follows:
The proportion by mass of the elements participating in the composition of a substance is always constant and independent of the chemical process by which the substance is obtained.