Knowledge database: Basic laws of chemistry: Avogadro's law

As mentioned in the chapter concerning the law of combining volumes, initially it was thought that all gases of equal volumes, within the same conditions, contain the same number of atoms.

This however could not explain even some of the simplest reactions such as the reaction of hydrogen and chlorine. For example, one liter of hydrogen reacts with one liter of chlorine to give 2 liters of hydrogen chloride.

Taking into account the above mentioned theory, this would mean that one chlorine atom and one hydrogen atom form two particles of hydrogen chloride (each with one hydrogen atom and one chlorine atom) and that can not be possible. Now we come to the conclusion that in this case, the gas particles of the reagents are not atoms, but small groups of atoms (in this case, diatomic molecules).

This law was discovered by the Italian physicist Amedeo Avogadro and is defined as follows: equal volumes of different gases, at the same temperature and pressure, contain the same number of molecules.