Avogadro's Law
Equal volumes of an ideal gas contain equal numbers of molecules, if both volumes are at the same temperature and pressure. For example, 1 L of ideal gas contains twice as many molecules as 0.5 L of ideal gas at the same temperature and pressure.
It is, in fact, only true for ideal gases.
See also: Avogadro, Armedeo, Dalton′s Law of Partial Pressures.
Subjects: Physics