Topics of this article
- 1 - Gay-Lussac's volumetric law
- 2 - Proust's laws (Law of constant proportions or law of definite proportions)
Gay-Lussac volumetric law
Gay Lussac was a French physicist and chemist who is known today for his scientific contributions, and one of them is the Law of Gases.
Another great contribution by Gay-Lussac is his Volumetric Law, where he states that under the same conditions of temperature and pressure, the volumes of gases participating in a reaction have a relationship between whole numbers and small.
In Chemistry and Physics Gay-Lussac's Law is a perfect gas law: under constant volume, the pressure of a constant amount of gas increases proportionally with temperature:
P = K
T
where:
P is the pressure of the gas
T is the temperature of the gas (in kelvins)
k is a constant
We can sum it up in a single statement:
The volume ratio of the gases in a reaction (volumes measured at the same pressure and temperature) is constant and of small whole numbers.
Example:
Decomposition of water vapor: this thesis was published in 1808, by Gay-Lussac, and involves the reaction between hydrogen and oxygen.
| Experience | Decomposed volume of water vapor | Volume of hydrogen gas produced | Volume of oxygen gas produced |
| 1º | 1L | 1L | 0.5L |
| 2º | 2L | 2L | 1L |
| 3º | 4L | 4L | 2L |
volume ratio
Vwater vapor: Vhydrogen: Voxygen = 2: 2: 1
Do not stop now... There's more after the publicity ;)
Proust's laws (Law of constant proportions or law of definite proportions)
Proust made qualitative and quantitative analyzes of numerous substances acquired by different processes and verified that the same substance always had the same qualitative composition and quantitative.
Thus, any sample of sodium chloride always had sodium and chlorine combined in the same mass ratio. Then came the law:
The same substance always has the same elements whose masses are in constant proportion.
| Experience | Mass of decomposed water | Mass of hydrogen obtained | Mass of oxygen obtained |
| 1º | 18g | 2g | 16g |
| 2º | 72g | 8g | 64g |
| 3º | 90g | 10g | 80g |
Comparing the ratio between the masses of hydrogen and oxygen in each experiment, we have:
Conclusion:
The pure substance water is formed of hydrogen and oxygen, always in the constant proportion of 1/8 by mass. Proust's law was later extended to any chemical reaction.
In a chemical reaction, there is a constant ratio between the masses of the participating substances.
Outlining:
By Líria Alves
Graduated in Chemistry
Would you like to reference this text in a school or academic work? Look:
SCHOOL, Team Brazil. "Laws of Gay-Lussac and Proust"; Brazil School. Available in: https://brasilescola.uol.com.br/quimica/leis-gay-lussac-proust.htm. Accessed on July 08, 2023.
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