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Concept
Loi de Gay-Lussac
Résumé
Gay-Lussac's law usually refers to Joseph-Louis Gay-Lussac's law of combining volumes of gases, discovered in 1808 and published in 1809. However, it sometimes refers to the proportionality of the volume of a gas to its absolute temperature at constant pressure. The latter law was published by Gay-Lussac in 1802, but in the article in which he described his work, he cited earlier unpublished work from the 1780s by Jacques Charles. Consequently, the volume-temperature proportionality is usually known as Charles's Law.
The law of combining volumes states that when gases chemically react together, they do so in amounts by volume which bear small whole-number ratios (the volumes calculated at standard temperature and pressure).
The ratio between the volumes of the reactant gases and the gaseous products can be expressed in simple whole numbers.
For example, Gay-Lussac found that two volumes of hydrogen and one volume of oxygen would react to form two volumes of gaseous water. Based on Gay-Lussac's results, Amedeo Avogadro hypothesized that, at the same temperature and pressure, equal volumes of gas contain equal numbers of molecules (Avogadro's law). This hypothesis meant that the previously stated result
2 volumes of hydrogen + 1 volume of oxygen = 2 volume of gaseous water
could also be expressed as
2 molecules of hydrogen + 1 molecule of oxygen = 2 molecule of water.
It can also be expressed in another way of example,
100 mL of hydrogen combine with 50 mL of oxygen to give 100 mL of water vapour.
Hydrogen(100 mL) + Oxygen(50 mL) = Water(100 mL)
Thus, the volumes of hydrogen and oxygen which combine (i.e., 100mL and 50mL) bear a simple ratio of 2:1.
The law of combining gases was made public by Joseph Louis Gay-Lussac in 1808. However, Avogadro's hypothesis was not initially accepted by chemists until the Italian chemist Stanislao Cannizzaro convinced the First International Chemical Congress in 1860.
In the 17th century Guillaume Amontons discovered a regular relationship between the pressure and temperature of a gas at constant volume.
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