State
(a) Gay-Lussac's law of combining volumes.
(b) Avogadro's law.
(a) Gay-Lussac's law of combining volumes states that the gases always combine in simple ratio of their volumes, and also to the volume of the gaseous product, when all the volumes are measured at constant temperature and pressure.
For example, the hydrogen and chlorine gas reacts to give hydrogen chloride gas and is represented as:
H2 (g) + Cl2 (g) 2HCl (g)
The volume ratio in which the hydrogen and chlorine gas (reactants) consumes and produces hydrogen chloride (product) is always equal to 1:1:2.
(b) Avogadro's law states that equal volumes of all gases contain the same number of molecules under same temperature and pressure; i.e., one litre of hydrogen gas contains the same number of molecules as one litre of oxygen gas at same temperature and pressure.